Biochimie, 1977, 59(11-12), 947 - 9 {The autonomic transfer of mitochondrial factors (cytoduction) during crossing of Saccharomyces cerevisiae cells}; Zakharov IA et al.; When crossing the genetically marked yeast strains obtained from the Gif collection we observed the appearance of haploid nucleo-cytoplasmic hybrids carrying the 3 nuclear markers of the rho- parent and the mitochondrial markers (rho+ ER CR) of the other parent . The frequency of such cytoduction was about 1 per cent . The mitochondrial markers ER and CR were transmited to cytoductants together and did not segregate . The possible mechanisms of the cytoduction and its significance are discussed. Genetika, 1977, 13(7), 1237 - 45 {Multiple mutants of Saccharomyces cerevisiae . IV . Mutability of yeast cultures at different growth stages}; Aref'eva AIa et al.; Mutability at different stages of culture growth in liquid media of two yeast strains, which revealed a property of "multiple mutability" and one strain of wild type for this property, was studied . One strain that possessed the property of "multiple mutability" showed at stationary phase a very high frequency of mutability, which reached 3.5% . It was found that multiple mutants arose in both strains, that possessed the property under investigation, at lag- and log-growth phases, and only in one strain -- at the stationary phase of growth . The possible reasons of "multiple mutability" display are discussed. Mikrobiologiia, 1977 Jan-Feb, 46(1), 161 - 4 {Cytomorphologic characteristics of Saccharomyces cerevisiae and Candida utilis as an index of the physiologic state of the culture}; Vrana D et al.; The dimensions of daughter cells without scars, and of mother cells with 1--4 scars, of Saccharomyces cerevisiae and Candida utilis were studied in the one-stage chemostat at D equal to 0.05, 0.1, 0.25, and 0.35 hr-1 . The average dimensions of the cells increased with the specific growth rate . At low values of the specific growth rate, "immature" daughter cells separate and attain reproductive ability as independent individual organisms . A twofold increase in the biomass of yeast cells occurs at the account of growth of the buds and small daughter cells. Mutat Res, 1977 Jan, 42(1), 45 - 50 Genetic effects of some new bifunctional and water-soluble analogs of the anti-cancer agent 1,3-bis(2-chloroethyl)-1-nitrosourea (BCNU) in Saccharomyces cerevisiae; Siebert D et al.; A series of 1,1'-polymethylenebis-3-(2-chloroethyl)-3-nitrosoureas, 1-(omega-hydroxyalkyl)-3-(2-chloroethyl)-3-nitrosoureas, 1,1'(4-methyl-m-phenylenebis)-3-(2-chloroethyl)-3-nitrosourea, 2-{3-(2-chloroethyl)}-3-nitrosoureido-2-deoxy-D-glycopyranose (chlorozotocin and 1-(2-methanesulfonyloxyethyl)-3-(2-chloroethyl)-3-nitrosurea were examined for their genetic activities . BCNU was simultaneously tested as an established, clinically used reference compound . A diploid strain of Saccharomyces cerevisiae, heteroallelic at the gene loci ade2 and trp5, was used as a test system for the induction of mitotic gene conversion (intragenic recombination) . All compounds showed strong genetic effects . In the series of aliphatic bifunctional nitrosoureas, 1,1'-ethylenebis-3-(2-chloroethyl)-3-nitrosourea (1) was the most active compound . The water-soluble derivatives, including chlorozotocin, displayed all genetic effects of the same order of magnitude . There was no correlation between genetic activity and chemotherapeutic potential of the test compounds. J Bacteriol, 1977 Jan, 129(1), 97 - 100 Fractionation of Saccharomyces cerevisiae cell populations by centrifugal elutriation; Gordon CN et al.; An exponential population of Saccharomyces cerevisiae cells was fractionated by centrifugal elutriation, using water as the elutriating liquid . Evidence that the population had been fractionated according to age in the cell cycle was obtained by examining the fractions for their size distribution, their microscopic appearance after Giemsa staining, and their ability to initiate synchronous growth. J Bacteriol, 1977 Jan, 129(1), 47 - 51 Size and turnover of polyadenylic acid-containing ribonucleic acids in a fragile mutant of Saccharomyces cerevisiae; Venkov PV et al.; Ribonucleic acid-containing polyadenylic acid {poly(A)+-RNA} was studied in lysates from an osmotic-sensitive mutant of Saccharomyces cerevisiae characterized by low nuclease activity . The poly(A)+-RNA fraction, analyzed by electrophoresis in polyacrylamide-formamide gels, constitutes a heterogeneous population of molecules, with molecular weights ranging from 0.2 X 10(6) to 3 X 10(6) and having an average of 1.2 X 10(6) . The turnover rate of poly(A)+-RNA was determined by the decay of radioactivity after a cold uracil chase, and the observed half-life of 21 min corresponds to about 10% of the cell doubling time . Poly(A)+-RNA was analyzed by gel electrophoresis under denaturing and non-denaturing conditions . A correlation was established between the apparent secondary structure and the turnover rate of poly(A)+-RNA species. Folia Microbiol (Praha), 1977, 22(1), 19 - 29 Activities of mitochondrial enzymes during aerobic synchronous growth of aerobically and anaerobically grown Saccharomyces cerevisiae; Nejedly K et al.; The mitochondrial enzymes cytochrome-c:O2-oxidoreductase (E.C.1.9.3.1), NADH:cytochrome-c-oxidoreductase (E.C.1.6.2.1), NADH: ferricyanide oxidoreductase (E.C.1.6.2.99), L-malate hydrolase (E.C.4.2.1.2) and L-malate:NADH-oxidoreductase (E.C.1.1.3.7) increase their activities during the aerobic synchronous growth of aerobically grown Saccharomyces cerevisiae in discrete steps and only once during the cell cycle . An identical phenomenon was observed during the aerobic synchronous growth of anaerobically grown yeast . The mechanism of completization of mitochondrial membranes is thus likely to be discontinuous and the same during both mitochondrial multiplication and the conversion of promitochondria to fully functioning mitochondria. C R Seances Soc Biol Fil, 1977, 171(4), 879 - 82 {Autoradiography of the exchanges that can occur between murine sarcoma cells (BP 8) and yeast cells (Saccharomyces cerevisiae, complete or protoplast)}; Miegeville M et al.; We can tell after observing the resulting negative that yeasts are able, in our experimental conditions, to collect a sequence of ADN and of ARN proceeding from the cancerous cells . Then, those yeasts could turn their synthesis towards the production of new materials . If those informed yeasts were introduced into a mouse, they would induce at the level of the immunocompetent cells a specific immunizing antitumoral power. C R Seances Soc Biol Fil, 1977, 171(4), 814 - 7 {Metabolism of nucleoside Y in a mutant strain auxotrophic for guanine (gua 2 su+) of Saccharomyces cerevisiae}; Lacharme J et al.; The study of free nucleoside Y metabolism in a mutant strain of Saccharomyces cerevisiae seems to indicate that this component is not only provided by t-RNA Phe turnover . A peculiar physiologic activity-mitogenic type - may be connected with this observation. Eur J Biochem, 1976 Dec 11, 71(2), 393 - 8 Catalase biosynthesis in yeast: formation of catalase A and catalase T during oxygen adaptation of Saccharomyces cerevisiae; Zimniak P et al.; Catalase A from Saccharomyces cerevisiae and its biosynthetic precursors can specifically be immunoprecipitated from extracts obtained from yeast cells grown in the presence of L-{3H}leucine or 59FeCl3 . The enzyme and its precursors recognized by a specific antiserum are absent from anaerobic cells . During oxygen adaptation of yeast pre-grown on 0.3% glucose under anaerobic conditions catalase A is formed via a heme-less precursor, probably the apomonomer of the protein, and a heme-containing intermediate . When cells are grown in the presence of Tween 80 the amount of catalase A, but not of catalase T, increases 4-fold . Comparison of the mode of synthesis of catalase T and A shows that no precursor-product relationship exists between the two proteins. Mol Gen Genet, 1976 Dec 8, 149(2), 125 - 30 Recombined molecules of mitochondrial DNA obtained from crosses between cytoplasmic petite mutants of Saccharomyces cerevisiae: the stoichiometry of parental DNA repeats within the recombined molecule; Michaelis G et al.; We have studied recombination between repetitive mitochondrial DNAs from cytoplasmic petite mutants of Saccharomyces cerevisiae . Mitochondrial DNA was isolated from two parental p- mutants, carrying respectively the CR and the ER mitochondrial genetic markers, and from two p- CRER diploid genetic recombinants . These two recombinants, obtained from the same parental petites, differ in their degrees of suppressiveness . The p- mitochondrial DNAs were analyzed by DNA-DNA hybridization, high resolution melting and reassociation kinetics . It was found that the repeating unit of the CR parental p- DNA is 3 to 4 times longer than that of the ER parent . There is very little sequence homology between these two p- mitochondrial DNAs and almost all parental sequences are integrated into the recombined molecules . Mitochondrial DNA from both types of recombinants seems to contain the two parental repeating units in the ratio 1:1. Arch Microbiol, 1976 Dec 1, 111(1-2), 13 - 9 Correlation among turnover of nucleic acids, ribonuclease activity and sporulation ability of Saccharomyces cerevisiae; Tsuboi M; The turnover of nucleic acids and changes in ribonuclease activity during sporulation of Saccharomyces cerevisiae were studied . In the sporulating strains, 37-58% of vegatatively synthesized RNA were degraded during the sporulation process . The degree of degradation of vegetative RNA was proportional to the sporulation ability . In the non-sporulating strains, the degradation of vegetative RNA was less than 28% in the sporulation medium . Accompanied by the degradation of vegetative RNA, a ribonuclease activity increased several times during sporulation . We have found a close relation among the sporulation rate, the degree of the degradation of vegetative RNA and the increase in ribonuclease activity in the sporulation medium, using cells of which sporulation ability was repressed by changing the age or carbon source in various degrees. Mutat Res, 1976 Dec, 41(2-3), 241 - 8 The relation between repair of DNA and radiation and chemical mutagenesis in Saccharomyces cerevisiae; Prakash L; The effect of various genes involved in DNA repair functions on radiation and chemical mutagenesis in Escherichia coli is discussed and compared to similar studies done in yeast . Results of the effect of various genes conferring radiation-sensitivity on mutation induction in yeast are presented and related to current ideas of mutagenesis. J Gen Microbiol, 1976 Dec, 97(2), 323 - 9 Plasma membrane ultrastructural differences between the exponential and stationary phases of Saccharomyces cerevisiae as revealed by freeze-etching; Takeo K et al.; Ultrastructural changes in the plasma membrane of Saccharomyces cerevisiae during the exponential and stationary growth phases were studied by freeze-etching . In the exponential phase, plasma membrane-intercalated particles were distributed randomly . In the stationary phase, several areas of the plasma membrane showed a hexagonal arrangement of particles; these areas appeared to increase with the age of the culture . The polarity of the particles also changed partially: the E-face of the plasma membrane was only sparsely embedded with particles in exponential phase cells, but relatively densely embedded in stationary phase cells . Invaginations of the plasma membrane on the P-face were devoid of particles during both growth phases . Invaginations of the E-face were sparsely embedded with particles in exponential phase cells, but densely embedded with particles in stationary phase cells. Genetics, 1976 Dec, 84(4), 697 - 721 Gene conversion and intragenic recombination at the SUP6 locus and the surrounding region in Saccharomyces cerevisiae; Dicarprio L et al.; Spontaneous secondary mutations of the ochre suppressor SUP6 were selected in a haploid strain of Saccharomyces cerevisiae . Unselected tetrads were dissected from crosses heterozygous for one of three allleles of SUP6 and for three other loci in this region which span a length of 14 map units (his2, cdc14 and met10) . The study showed that all of these markers were characterized by high frequency of meiotic gene conversion and long conversion lengths which frequently extended into adjacent marked loci . Despite the high conversion frequency of SUP6, recombination between alleles of this locus reached a maximum frequency of only 2 x 10(-3) protrophs/spore . Although the allelic recombination frequencies were not distance dependent and consequently could not be used to order the alleles, the inequality between the two recombinant outside marker combinations among selected intragenic recombinants produced an internally consistent map of the suppressor locus . Recombination at SUP6 (whether detected as conversion in tetrads or the production of recombinants among random spores) was accompanied by significantly less than 50% outside marker recombination. Proc Natl Acad Sci U S A, 1976 Dec, 73(12), 4623 - 7 Genetic analysis of a transposable suppressor gene in Saccharomyces cerevisiae; Laten HM et al.; We have demonstrated in Saccharomyces cerevisiae the transposition of a gene coding for an efficient ochre (UAA) suppressor from a centromere-linked site on chromosome III to two new sites in the yeast genome . One site is on chromosome VI, very close to, if not allelic with, SUP11, one of eight genes coding for a tyrosine-inserting suppressor . The second site is on chromosome III, unlinked to the centromere and distal to the mating type locus . This site is very close to those mapped for the recessive lethal amber suppressors, SUP-RL1 and SUP61. J Bacteriol, 1976 Dec, 128(3), 855 - 7 Regulation of thiamine transport in Saccharomyces cerevisiae; Iwashima A et al.; Yeast cells were found to be repressed for the uptake of both thiamine and pyrithiamine by growth with exogenous thiamine, and they appeared to regulate the activity of the binding protein for these compounds. J Biol Chem, 1976 Nov 25, 251(22), 7278 - 80 Selective inhibition of protein synthesis initiation in Saccharomyces cerevisiae by low concentrations of cycloheximide; Cooper TG et al.; We have previously determined the amounts of time required to complete various macromolecular synthetic processes needed for induction of allophanate hydrolase in Saccharomyces cerevisiae . This information provided a means of testing, in vivo, an early hypothesis suggesting that cycloheximide inhibited the initiation as well as elongation steps of protein synthesis . Our data suggest that initiation of protein synthesis in yeast may be inhibited by low concentrations of cycloheximide which do not significantly affect polypeptide chain elongation. Mol Gen Genet, 1976 Nov 17, 148(3), 251 - 61 A novel class of Saccharomyces cerevisiae mutants specifically UV-sensitive to "petite" induction; Moustacchi E et al.; A mutant of Saccharomyces cerevisiae has been isolated which, though exhibiting a normal response to nuclear genetic damage by ultraviolet light (UV), is more sensitive than its wild type specifically in the production of the cytoplasmic (rho-) mutation by this agent . Some of the features of this mutation which has been designated uvsrho 5 are: i) The mutation is recessive, it exhibits a Mendelian, and hence presumably nuclear, pattern of segregation, but manifests its effects specifically and pleiotropically on mitochondrial functions . ii) Mutant cells resemble their wild type parents in a) growth characteristics on glucose; b) in their UV induced dose response to lethality or nuclear mutation and c) the ability of their mitochondrial genome, upon mating with appropriate testers, of transmitting and recombining various markers, albeit with enhanced efficiency . Similarly, d) they are able to modulate the expression of mitochondrial mutagenesis by ethidium bromide . Thus their mitochondrial DNA appears genetically as competent as that of the wild type . iii) Mutant cells differ from their wild type parents in a) growth characteristics on glycerol; b) susceptibility to induction of the mitochondrial (rho-) mutation by various mutagens, in that the rate of spontaneous mutation is slightly and that by UV is significantly enhanced, whild that by ethidium bromide is greatly diminished . Conversely, c) modulating influences resulting in the repair of initial damage are diminished fro UV and stimulated in the case of Berenil . iv) The amount of mitochondrial DNA per cell appears elevated in the mutant, relative to wild type, and its rate of degradation subsequent to a mutagenic exposure to either UV or ethidium bromide is diminished . v) A self-consistent scheme to account for this and all other information so far available for the induction and modulation of the (rho-) mutation is presented . In a previous study it was shown that some nuclear mutants of Saccharomyces cerevisiae, more sensitive to lethal damage induced by ultraviolet light (rad) than their parent wild type (RAD), also exhibit a concomitant modification in sensitivity to both nuclear and cytoplasmic genetic damage (Moustacchi, 1971) . However, another class of rad mutants respond to the induction of the cytoplasmic "petite" also designated as rho- (or rho-) mutation by UV in a manner indistinguishable from that of the RAD strain . One possible interpretation of this last observation is that some of the steps in the expression of the UV damage on mitochondrial (mt)DNA may be governed by other nuclear and cytoplasmic genetic determinants, the products of which may then act specifically on mitochondrial lesions . If this assumption is correct, it should be possible to find mutants with a normal response to nuclear damage but specifically UV-sensitive towards induction of (rho-)... Mol Gen Genet, 1976 Nov 17, 148(3), 233 - 41 Restriction endonuclease analysis of ribosomal DNA from Saccharomyces cerevisiae; Cramer JH et al.; The size and degree of homogeneity of the repetitive units in purified ribosomal DNA (gamma DNA) from Saccharomyces cerevisiae have been analyzed by restriction endonuclease digestion and heteroduplex mapping . Digestion of the gamma DNA with EcoRI yields seven fragments, digestion with Hind II+III yields five fragments, digestion with Hind III alone yields two fragments, and digestion with Sma I yields one fragment . The sum of the fragment molecular weights after digestion with each of the endonucleases is 5.5-5.6 x 10(6) . When the DNA strands of the Sma I fragment are dissociated and reannealed, only homoduplexes are formed . We have concluded from these results that the repeating units in yeast ribosomal DNA are 5.6 x 10(6) datons and are homogeneous in size and composition. Mutat Res, 1976 Nov, 37(2-3), 201 - 12 Genetic effects induced in Saccharomyces cerevisiae by cyclophosphamide in vitro without liver enzyme preparations; Mayer VW et al.; Cyclophosphamide induced forward mutation in Saccharomyces cerevisiae strain S288C and mitotic recombination in strains D3 and D5 but not in strain D4 . The yeast cells were treated with the compound in phosphate buffer without recourse to metabolic activation protocols . Elevation of the treatment temperature increased the genetic activity of cyclophosphamide . Respiration-deficient isolates of strains S288C and D3 were more sensitive than the respiratory competent parent strains were for inducing forward mutation and mitotic recombination, respectively . Cyclophosphamide was incubated in phosphate buffer alone for increasing time intervals; strain D3 cells were added to aliquots for each time interval and incubated for an additional 30 min . The frequency of induced recombination increased as the time of compound incubation increased, showing that spontaneous degradation of cyclophosphamide to genetically active breakdown products was responsible for the genetic damage induced in the yeast cells. J Cell Sci, 1976 Nov, 22(2), 219 - 42 Electron-microscopic study of the spindle and chromosome movement in the yeast Saccharomyces cerevisiae; Peterson JB et al.; Mitosis in yeast Saccharomyces cerevisiae was investigated in thick (0-25-I mum) serial sections with a high voltage electron microscope and in preparations of spheroplasts spread on a water surface . Spindle microtubules originate from a plaque-like structure called the spindle pole bosis the SPB duplicates and a set of long and short microtubules develops on each SPB . The spindle arises as the SPBs separate on the nuclear membrane adense and are not individually visible . Genetic studies, however, have indicated that there are 17 linkage groups . The number of microtubules was determined in diploid and haploid spindles on serial stereo micrographs . In diploid mitosis about 40 microtubules issue from a SPB . Most are non-continuous and often they are visibly associated with a chromatin fibre . The spindle in haploid cells is similar except that the number of microtubules is about half that in diploid cells and the SPB is smaller . The pole-to-pole microtubules vary in number from spindle to spindle, but in each case enough microtubules are present to account for each linkage group being associated with a single non-continuous microtubule . We conclude that mitosis in yeast is comparable in its general aspect to that observed in typical eukaryotes. J Bacteriol, 1976 Nov, 128(2), 689 - 91 Adenosine utilization in cordycepin-sensitive mutants of Saccharomyces cerevisiae; Anderson JM et al.; A purine-requiring, wild-type yeast strain was cordycepin resistant and failed to grow in medium containing adenosine; in contrast, a cordycepin-sensitive mutant (also purine requiring) grew well in medium containing adenosine . The cordycepin-sensitive mutant incorporated {8-14C}adenosine at nine times the wild-type rate, and adenosine completely fulfilled the purine requirement of the cells . Exogenous adenosine rapidly entered the mutant cells, apparently as free nucleoside, and was phosphorylated; uptake displayed concentration-dependent saturation kinetics (Km, 6 mM) . Within 10 min 14C radioactivity was being incorporated into nucleic acids. Mol Gen Genet, 1976 Oct 18, 148(2), 165 - 70 The induction of mitotic gene conversion by chemical and physical mutagens as a function of culture age in the yeast, Saccharomyces cerevisiae; Davies PJ et al.; Cultures of yeast progressing from the exponential to the stationary phase of growth show increased resistance to the lethal effects of the chemical mutagens nitrous acid, ethyl methane sulphonate and mitomycin C and increased sensitivity to the lethal effects of UV light . Induced mitotic intragenic recombination produced by gene conversion also shows variation in its response to the growth phase after mutagen treatment . Higher frequencies of recombination per surviving cell were found after nitrous acid and ethyl methane sulphonate treatment of stationary phase cells whereas identical frequencies were produced by UV and mitomycin C treatment in both growth phases . The results were consistent with the hypothesis that the more nitrous acid and ethyl methane sulphonate resistant stationary phase cells were more active in postreplication repair . The sensitivity of exponential phase cells to nitrous acid and ethyl methane sulphonate may result from both increased mutagen uptake and reduced postreplication repair activity . In contrast, irrespective of growth phase all cells surviving UV and mitomycin C treatment appear to have undergone identical levels of post-replication repair. J Gen Microbiol, 1976 Oct, 96(2), 263 - 8 Amino-acid pool composition of Saccharomyces cerevisiae as a function of growth rate and amino-acid nitrogen source; Watson TG; The composition of the amino-acid pool of Saccharomyces cerevisiae is markedly influenced by the amino-acid nitrogen source . The yeast tends to accumulate the amino acid supplied and those closely related to it metabolically . A relatively high concentration of glutamic acid is maintained in the pools of all cultures irrespective of the nitrogen source, reflecting the central role of glutamic acid in nitrogen metabolism . The total amino-acid pool concentration increases as a function of growth rate, although differences exist in the behaviour of individual amino acids. Proc Natl Acad Sci U S A, 1976 Oct, 73(10), 3651 - 5 A mutant of Saccharomyces cerevisiae defective for nuclear fusion; Conde J et al.; A mutant unable to fuse nuclei during mating has been isolated from standard wild-type Saccharomyces cerevisiae . Tetrad analysis of the mutation responsible for this defect (kar1-1) shows that it segregates as a single Mendelian factor . The defect kn kaf1-1 appears to be nuclear limited . Cytological and genetic evidence shows that in this mutant the events associated with zygote formation are normal until the point of nuclear fusion . The consequence of this defect is the formation of a multinucleate zygote which in subsequent divisions can segregate heterokaryons and haploid heterplasmons. J Bacteriol, 1976 Oct, 128(1), 49 - 55 Regulation of arginine biosynthesis in Saccharomyces cerevisiae: isolation of a cis-dominant, constitutive mutant for ornithine carbamoyltransferase synthesis; Messenguy F; A cis-dominant mutation linked to argF, the structural gene specifying ornithine carbamoyltransferase, and affecting the control of the synthesis of this enzyme has been obtained . The level of ornithine carbamoyltransferase in this mutation is depressed and less repressible by addition of L-arginine than it is in the wild-type strain . Of 38 tetrads analyzed, resulting from a cross of a strain harboring this mutation with a strain carrying an argF- mutation, none was a tetratype or a nonparental ditype . This operator mutation helps to define a negative mode of control of the synthesis of the arginine biosynthetic enzymes, as had been suggested earlier upon the isolation of argRI- (arg80), argRII- (arg81), and argRIII- (arg82) specific regulatory mutations. Genetics, 1976 Sep, 84(1), 27 - 42 A study of the transmission and structure of double stranded RNAs associated with the killer phenomenon in Saccharomyces cerevisiae; Sweeney TK et al.; Killer strains contain two double stranded RNAs, L and M.The M dsRNA appears to be necessary for production of a toxin and for resistance to that toxin . Mutant strains have been found that are defective in their ability to kill and in their resistance to toxin . These sensitive, non-killer strains have altered dsRNA composition . One class has no M dsRNA.Another class of sensitive, non-killers called suppressives has no M dsRNA but instead has smaller dsRNAscalledS.Indiploidsresulting from a cross of a wild-type killer by a suppressive the transmission of the M dsRNA is suppressed by the S dsRNA.When a suppressive is crossed by a strain with no M dsRNA, the diploids and all four meiotic spores have the S dsRNA characteristic of the parental suppressive strain . Suppressive strains do not suppress each other . Intercrosses between two different suppressives yields diploids with both parental S dsRNAs . These two S dsRNAs are transmitted to all 4 meiotic progeny . Another class of mutants has been found which is defective for one of the traits but retains the other . One type, temperature-sensitive killers, has a normal dsRNA composition but is unable to kill at 30 degrees . The other type, immunity-minus, has a complex dsRNA pattern . The immunity-minus strain is extremely unstable during mitotic growth and segregates several different types of non-killers . Analysis of the dsRNAs from wild type and the mutants by electron microscopy shows that the L, M, and S dsRNAs are linear . All strains regardless of killer phenotype appear to have the same size L dsRNA. Arch Microbiol, 1976 Sep 1, 109(3), 221 - 5 Inactivation by glucose of phosphoenolpyruvate carboxykinase from Saccharomyces cerevisiae; Gancedo C et al.; Phosphoenolpyruvate carboxykinase showed high activity in Saccharomyces cerevisiae grown on gluconeogenic carbon sources . Addition of glucose to such cultures caused a rapid loss of the phosphoenolpyruvate carboxykinase activity . Fructose or mannose had the same effect as glucose, while 2-deoxyglucose or galactose were without effect . The inactivation was an irreversible process, since the regain of the activity was dependent of de novo protein synthesis . Cycloheximide did not prevent inactivation . All strains of the genus Saccharomyces tested showed inactivation of their phosphoenolpyruvate carboxykinase upon addition of glucose; this behaviour was not restricted to this genus. J Gen Microbiol, 1976 Sep, 96(1), 165 - 74 Role of wall phosphomannan in flocculation of Saccharomyces cerevisiae; Jayatissa PM et al.; Treatment with 60% hydrofluoric acid (HF) removed most of the phosphorus and small amounts of mannan, glucan and protein from walls of two non-flocculent strains (NCYC366 and NCYC1004) and two flocculent strains (NCYC1005 and NCYC1063) of Saccharomyces cerevisiae . Organisms of all strains showed increased flocculating ability following HF treatment . Flocculation of untreated organisms of NCYC1005 and NCYC1063, and of HF-treated organisms of all four strains, declined appreciably when they were washed in deionized water, with or without EDTA, and the flocculation was measured in deionized water instead of in 0-05 M-sodium acetate containing Ca2+ . Treatment with 1,2-epoxypropane also caused a decrease in the flocculating ability of these organisms . Extracting the lipids from organisms of strains NCYC366 and NCYC1004 had no effect on their flocculating ability, but decreased the flocculating ability of organisms of strains NCYC1005 and NCYC1063 . pH-electrophoretic mobility curves of untreated and HF-treated organisms confirmed the loss of wall phosphate by HF treatment, and indicated that HF treatment had little effect on the content of protein carboxyl groups in the outer wall layers . Mannose at 0-22 M completely prevented floc formation by organisms of strain NCYC1063; but, even at 0-33 M, it had very little effect on floc formation by HF-treated organisms of strains NCYC366 and NCYC1063 . Organisms of all four strains bound fluorescein-conjugated concanavalin A to the same extent after treatment with HF as before, but this treatment led to a greatly diminished binding of of fluorescein-conjugated antiserum raised against organisms of strain NCYC366 . The results indicate that phosphodiester linkages in yeast-wall mannan are not involved in bride formation through Ca2+ during floc formation and that this arises principally through carboxyl groups. Biochim Biophys Acta, 1976 Aug 23, 441(2), 294 - 301 Isolation and characterization of the liponucleotides of Saccharomyces cerevisiae; Schneider EG et al.; The liponucleotide fraction of Saccharomyces cerevisiae was isolated from cells grown on tritiated uracil and identified as CDPdiacylglycerol on the basis of (1), its behavior as a single compound upon DEAE-cellulose and thin-layer chromatography; (2), its extreme lability to mild alkaline methanolysis; and (3), its hydrolysis by the CDPdiacylglycerol hydrolase of Escherichia coli to yield tritiated 5'-CMP . At most, only about 5% of yeast liponucleotide could be dCDPdiacylglycerol, in contrast to the presence of nearly equimolar amounts of CDP-and dCDPdiacylglycerols in E . coli . Although no CDPceramide could be detected in the liponucleotide fraction of this organism, the possibility still exists that it may be an intermediate in the biosynthesis of sphingolipids in systems yet to be examined. Mol Gen Genet, 1976 Aug 19, 147(2), 209 - 15 A simple method for the isolation and characterization of thymidylate uptaking mutants in Saccharomyces cerevisiae; Brendel M; The mutant tmpl--10ts which confers thermosensitive auxotrophy for thymidylate is employed for the selection of 5'-dTMP uptaking mutants . At the nonpermissive temperature yeast cells phenotypically wild type for thymidylate uptake can grow for only 3 to 4 generations in the presence of 10(-2) M 5'-dTMP . Thymidylate utilizing mutants (tum mutants) were isolated which can grow in the presence of 12 to 24 mug 5'-dTMP/ml . Genetical analysis revealed one of these mutant strains to be a double mutant, tuml tum2 . For normal growth haploid thymidylate auxotrophic strains require approximately 360 mug 5'-dTMP/ml when tuml and 24 mug 5'-dTMP when tum2 is present, respectively . Cells prototrophic for thymidylate (TMP) harbouring tuml tum2 will also take up 5'-dTMP and incorporate it specifically into their DNA . Thymidylate utilization in such strains is independent of functional mitochondria, as similar incorporation of labelled 5'-dTMP is found in isogenic strains with rho+, rho- and rho0 status . Optimal stimulation of the 5'-dTMP uptaking principle in haploid TMP strains is found at 4 mug5'-dTMP/ml when tuml and tum2 are present. Genetics, 1976 Aug, 83(4), 655 - 66 Mutators in Saccharomyces cerevisiae: MUT1-1, MUT1-2 and MUT2-1; Gottlieb DJ et al.; The purpose of this study was to characterize two mutator stocks of yeast which were induced and selected on the basis of high spontaneous reversion rates of the suppressible "ochre" nonsense allele lys1-1 . In the mutator stock VA-3, a single mutation, designated mut1-1, is responsible for the increase in the reversion rate of the ochre alleles lys1-1 and arg4-17 . In stock VA-105, there are two separate mutator mutations . Tetrad analysis data showed these two loci are loosely linked . Based on complementation data, one of these mutations is at the same locus as mut1-1 and designated mut1-2 . The second mutator of stock VA-105 was designated mut2-1 . All three mutators are recessive . Both mut1-1 and mut1-2 give a high mutation rate for ochre nonsense suppressor (SUP) loci, but not for the ochre nonsense alleles . On the contrary, the mutation rates of the ochre alleles are greatly reduced . With the mutant mut2-1 there were mutations at both the lys1-1 site and its suppressors; mut2-1 is as effective as mut1-2 but not as effective as mut1-1 in inducing reversions of a missense mutant, his1-7 . Neither mut1-1, mut1-2 nor mut2-1 were effective in inducing reversions of a putative frameshift mutation, hom3-10, or in inducing forward mutations to canavanine resistance. Genetics, 1976 Aug, 83(4), 645 - 53 Mutator activity of petite strains of Saccharomyces cerevisiae; Flury F et al.; Petite strains in Saccharomyces exhibit enhanced spontaneous mutation rates of nuclear genes regardless of whether they are cytoplasmically or nuclearly inherited, or whether or not the cytoplasmic petite strains have mitochondrial DNA . In petite strains, the mutation rate for the nonsense allele lys1-1 is enhanced by a factor of 3-6 and for the missense allele his1-7 by a factor of 2 as compared with their grande counterparts . The reversion of a third allele, the putative frameshift mutation, hom3-10, is not enhanced in a petite background . The results indicate that the spontaneous mutation rate of an organism can be altered by indirect intracellular influences. Proc Natl Acad Sci U S A, 1976 Aug, 73(8), 2828 - 32 Recombination in Saccharomyces cerevisiae: a DNA repair mutation associated with elevated mitotic gene conversion; Boram WR et al.; A mutant haploid strain of Saccharomyces cerevisiae has been isolated that is sensitive to the alkylating agent methyl methanesulfonate at a concentration of 0.01% (vol/vol) . The strain also shows sensitivities to x-rays and ultra-violet light, which cosegregate with sensitivity to methyl methanesulfonate as a single gene defect . An analysis of the sensitivity to ultraviolet light indicates that the mutation interferes with the excision of pyrimidine dimers . Diploids homozygous for the mutant gene exhibit elevated frequencies of spontaneous mitotic recombination at the ade6 locus . The results indicate that all the events are due to gene conversion . Mitotic recombination was also found to be elevated for three loci other than ade6 . Thus, the recombinational effect seems not to be locus specific . Linkage and allelism tests indicate that the mutation is an allele of the known radiation-sensitive gene rad18 . The various effects of this new rad18 allele (rad18-3) are discussed in terms of a defect in DNA repair mechanisms. Heredity, 1976 Aug, 37(1), 129 - 34 The genetic control of DS-RNA virus-like particles associated with Saccharomyces cerevisiae killer yeast; Mitchell DJ et al.; Previous results have indicated that laboratory strains of yeast possessing two types of dsRNA virus-like particles, V1 and V2, are capable of producing a killer toxin which kills sensitive strains . This paper reports on genetic crosses which correlate the presence of these particles both with a host nuclear gene +/-/mak1 and with the production of a killer toxin . The results show that: (i) V1 particles are inherited independently of the +/-/mak1 gene . (ii) V2 particles are present only in combination with those of V1 and the +/- allele of the +/-/mak1 nuclear gene. Mol Gen Genet, 1976 Jul 23, 146(2), 133 - 7 Cytoplasmic inheritance of antimycin A resistance in Saccharomyces cerevisiae; Michaelis G; Three antimycin resistant mutants of Saccharomyces cerevisiae are characterized genetically . The mutations have been shown to be cytoplasmically inherited by four criteria . The phenotype persists in diploids formed by a cross with a pO strain of yeast of the opposite mating type . Diploids heterozygous for the antimycin marker, however, show segregation of the resistance and sensitivity during mitosis . Tetrad analysis indicates a non-Mendelian segregation (4:0 and 0:4) of the mutations . The antimycin marker can be eliminated by ethidium bromide treatment under conditions that should have deleted all of the mitochondrial DNA. Mol Gen Genet, 1976 Jul 23, 146(2), 117 - 32 Mapping of mitochondrial genes in Saccharomyces cerevisiae . Populations and pedigree analysis of retention or loss of four genetic markers in Rho-cells; Schweyen RJ et al.; 1 . Retention or loss of mitochondrial markers CR321, OR1, PR454, TR (gene loci RIB1, OLI1, PAR1, TSM1 respectively has been analysed in a large number of ethidium bromide induced primary rho-clones . Retention of one or more of the four markers with a single clone was observed frequently, only 20 to 25% of clones were found to be (TOCOOOPO) . Primary clones retaining two or more of the four markers were found to be mixed, i.e . the primary rho- cell contained a heterogeneous population of variously deleted mitDNA molecules which segregated into different cell lines in the corresponding primary clone . 2 . A representative sample of the population of ethidium bromide induced rho- mutants has been analysed by a first subcloning performed after some 30 cell generations of vegetative multiplication in the abscence of the drug . At this level the heterogeneous population of mitDNA molecules, generated by the mutagenic treatment in the primary cell, has been sorted out . The cells forming secondary clones are thus essentially homoplasmic . In contrast to primary clones, genotypes of secondary clones therefore could be determined unambiguously, and the frequency of cell types can be regarded as a faithful representation of the frequency of mitDNA molecules . Retention of markers was low, in less than 2% of secondary clones one or several markers have been found . This observation has been interpreted as indicating that induction of rho-mutants by ethidium bromide is accompanied by deletion of very large sequences of mitDNA in a very large fraction of mitDNA molecules . 3 . Five individual rho-clones retaining the four markers TRCRORPR have been isolated and analysed for spontaneous deletion of one or several of these markers during successive subclonings (pedigree analysis) . High genetic stability (98-99.5% per cell generation) has been observed in these clones . 4 . A method has been developed allowing an unambiguous determination of the order of the four markers on a circular map . It is based on the concomitant loss of two markers and retention of the other two markers (double loss/double retention analysis) . The results of four out of five pedigrees of individual rho-clones analysed (spontaneous deletion) and the results of the analysis of populations of secondary rho-clones (ethidium bromide induced deletion) were in full agreement and the order of genes has been determined as being P-T-C-O-P . In the fifth pedigree results suggest an inversion of the T and C markers . 5 . Relative distances between pairs of markers have been derived from the frequencies of separation of markers by deletion and were found to be C-T less than C-O less than T-O less than T-P less than C-P less than O-P . Linkage of the four markers could be established, and distances calculated are additive . 6 . The general relevance of this approach of mapping by deletion and the methods used for the determination of order and distances of mitochondrial genes has been discussed . (ABSTRACT TRUNCATED) Mol Gen Genet, 1976 Jul 5, 146(1), 95 - 100 Differential effects of nalidixate on the cell growth of respiratory competent strains and cytoplasmic petite mutants of Saccharomyces cerevisiae; Carnevali F et al.; Sodium nalidixate inhibited the cell growth and division of several respiratory competent strains of Saccharomyces cerevisiae . A number of cytoplasmic petite strains (both spontaneous and induced by ethidium bromide) were shown to be more resistant to sodium nalidixate than the wild-type strains from which they were derived . There was considerable variation in sensitivity of different petites derived from the same wild-type . Usually petite strains which were induced by ethidium bromide were more resistant than spontaneously arising petites . The susceptibility of a wild-type strain to nalidixate was found to be least when the mitochondrial respiratory system was maximally repressed . It was also noted that sodium nalidixate (100 mug/ml) induced petite mutants. Mol Gen Genet, 1976 Jul 5, 146(1), 89 - 93 Effect of caffeine on the rho- -induction with ethidium bromide in Saccharomyces cerevisiae; Wolf K et al.; It is shown that caffeine antagonizes petite-induction with ethidium bromide under non-growth conditions when administered during or after mutagenic treatment . Caffeine itself is shown to be a petite-inducing agent when cells are grown in liquid glucose-complete-medium in the presence of the drug . A possible mode of action of caffeine in the ethidium bromide induced petite-mutagenesis is discussed. Mol Gen Genet, 1976 Jul 5, 146(1), 55 - 9 DNA Degradation and reduced recombination following UV irradiation during meiosis in yeast (Saccharomyces cerevisiae); Salts Y et al.; Irradiation of meiotic yeast cells with moderate doses of ultraviolet irradiation (1,600 erg/mm2) leads to the arrest of premeiotic DNA synthesis, massive (5-40%) DNA degradation, and a 40-50% loss of cell viability . In contrast, such doses of UV irradiation had a minor effect on viability (15-20% loss) of logarithmically growing cells, and no comparable DNA degradation was observed in irradiated synchronized vegetative cells . Meiotic recombination is also affected by UV irradiation . When administered at a stage comparable to meiotic prophase, low doses of irradiation result in a reduction in recombination frequency without significantly affecting cell viability. Mol Gen Genet, 1976 Jul 5, 146(1), 27 - 35 The effects of "cell age" upon the lethal effects of physical and chemical mutagens in the yeast, Saccharomyces cerevisiae; Parry JM et al.; Yeast cultures progressing from the exponential to the stationary phase of growth showed changes in cell sensitivity to physical agents such as UV light, heat shock at 52 degrees C and the chemical mutagens ethyl methane sulphonate, nitrous acid and mitomycin C . Exponential phree chemicals . The increased resistance of exponential phase cells to UV light was shown to be dependent upon the functional integrity of the RAD50 gene . Treatment of growing yeast cultures with radioactively labelled ethyl methane sulphonate indicated the preferential uptake of radioactivity during the sensitive exponential stage of growth . The results indicated that the differential uptake of the chemical mutagens was responsible for at least a fraction of the variations in cell sensitivity observed in yeast cultures at different phases of growth. Biokhimiia, 1976 Jul, 41(6), 1121 - 6 {Degradation of intracellular proteins at different stages of growth of Saccharomyces cerevisiae}; Bakalkin GIa et al.; The rate of degradation of intracellular proteins at different growth stages of Saccharomyces cerevisiae yeast was determined . It has been demonstrated that the rate of degradation of intracellular proteins increases 2--3-fold at the late exponential phase . The increase was accompanied by corresponding changes in the activities of yeast proteinases A and B . In the presence of specific yeast proteinase inhibitors (pepstatin and phenylmethylsulfonyl fluoride) the rate of protein degradation in vivo decreased . The intermediate products of cell protein degradation have been found . These TCA-insoluble products could be extracted by various solvent systems . Their subsequent brakdown was suppressed by specific proteinase inhibitors. Hoppe Seylers Z Physiol Chem, 1976 Jul, 357(7), 961 - 70 Localization of catalase A in vacuoles of Saccharomyces cerevisiae: evidence for the vacuolar nature of isolated "yeast peroxisomes"; Susani M et al.; The subcellular distribution of catalase A in the yeast Saccharomyces cerevisiae has been investigated . The enzyme was found to be bound to large particles, whereas most of the activity of catalase T was located in a 38 000 X g supernatant . Under various isolation conditions catalase A always showed a distribution among subcellular fractions virtually identical to that of two markers for vacuoles, proteinase B and alpha-mannosidase . More than 80 percent of the catalase A activity of a crude vacuole fraci-onercent of the catalase A activity of a crude vacuole fraction has been detected in purified vacuoles . Malate synthase, isocitrate lyase and glyoxylate reductase (NADP), three peroxisomal markers, showed a subcellular distribution significantly different from that of catalase A . It is concluded from these results that catalase A is specifically associated with the vacuoles of yeast . Like vacuoles, "peroxisomal" fractions isolated from yeast spheroplasts as described by Avers{1} contain only one catalase protein, catalase A . It could be shown by isopycnic and sedimentation velocity separations of crude mitochondrial fractions that catalase A in "peroxisomal" fractions is accompanied by considerable activities of proteinase B and alpha-mannosidase . From all our results it seems that the catalase-active particles isolated under such conditions are not typical peroxisomes but vesicles formed from vacuoles during the isolation procedure. Int J Radiat Biol Relat Stud Phys Chem Med, 1976 Jul, 30(1), 13 - 24 The genetic control of liquid-holding recovery and U.V.-induced repair resistance in the yeast, Saccharomyces cerevisiae; Parry EM et al.; Liquid-holding treatment in non-nutrient solutions after U.V.-exposure results in an increased resistance of wild-type (RAD) yeast cells to a second U.V.-treatment (repair resistance) . U.V.-sensitive (rad) mutants of yeast which show variation in their response to liquid-holding treatment and a second U.V.-dose-range have been classified into two groups . Mutants of Group 1 show increased viability after post-U.V.-liquid-holding treatment and show repair resistance . In contrast, mutants of Group 2 which show reduced viability during post-U.V.-liquid-holding treatment have the same U.V.-sensitivity, both before and after liquid-holding treatment . Genetic analysis of crosses of the rad mutants to wild-type cultures indicate that the phenotype of repair resistance to U.V.-treatment is under genetic control and depends on the presence of alleles of radiation sensitivity genes, which also confer the property of liquid-holding recovery. Mutat Res, 1976 Jul, 36(1), 49 - 66 The detection of monosomic colonies produced by mitotic chromosome non-disjunction in the yeast Saccharomyces cerevisiae; Parry JM et al.; A diploid yeast strain, D6 is described which monitors mitotic non-disjunction by the phenotypic expression of a set of coupled and recessive markers flanking the centromere of chromosome VII . These markers are not expressed in the heterozygous condition prevailing in D6 . The left arm of chromosome VII carries a tightly centromere linked marker, leu1 (leucine requirement), distal to leu1 in this order: trp5 (tryptophan requirement), cyh2 (recessive resistance to cycloheximide) and met 13 (requirement for methionine) . The right arm is marked with ade3 (simultaneous requirement for adenine and histidine) . D6 is homozygous for ade2 and consequently, forms red rather than the normally white colonies . It shows no requirement for the above amino acids and it is sensitive to cycloheximide . Unmasking of all the markers on chromosome VII leads to colonies that are white because ade3 sets a block preceding the ade2 block (which causes the accumulation of a precursor of the red pigment), they require leucine, tryptophan and methionine, and grow on media with cycloheximide . Cells are plated on a cycloheximide medium where red and white colonies are formed . Colonies of spontaneous origin were tested . The majority of the white colonies expressed all the recessive markers whereas only few of the red colonies expressed all the markers on the left arm of chromosome VII . Basically expression of recessive markers on both sides of the centromere can be explained as a result of two coincident events of mitotic crossing over . However, the frequency of colonies expressing centromere linked leu1 was 14 times higher among the white types than the red ones . This suggested that the white, cycloheximide resistant, leucine requiring colonies arose by mitotic non-disjunction and not only by two coincident mitotic crossing over events . Presumptive spontaneous monosomic segregants were placed on sporulation medium . Only 8 out of 30 isolates sporulated, which showed that these eight segregants were diploid at the time of sporulation . They could have arisen by two coincident crossover events or through restoration of a normal disomic condition after non-disjunction had occurred . The genetic data thus leaves us with only its statistical argument in favour of non-disjunction . Further confirmation of monosomic nature of the white cycloheximide resistant colonies was provided by the estimates of their DNA contents . Compared to the stock wild type diploids the presumptive monosomics showed a reduction in DNA content . We have utilized D6 to investigate the possible induction of mitotic non-disjunction after treatment with gamma rays, heat shock at 52 degrees C and ultraviolet irradiation . In all cases white, cycloheximide resistant colonies were produced at levels significantly higher than that found in untreated cultures . In order to detect the production of monosomic cells, treated cultures were grown for 48 h in non-selective medium after exposure to allow for "expression" of the monosomic condition. J Bacteriol, 1976 Jul, 127(1), 67 - 75 Fragility of plasma membranes in Saccharomyces cerevisiae enriched with different sterols; Hossack JA et al.; Saccharomyces cerevisiae NCYC 366, grown under strictly anaerobic conditions to induce requirements for an unsaturated fatty acid (supplied by Tween 80) and a sterol, contained free sterol fractions enriched to the extent of 67 to 93% with the exogenously supplied sterol (campesterol, cholesterol, 7-dehydrocholesterol, 22, 23-dihydrobrassicasterol, beta-sitosterol, or stigmasterol) . Cells enriched in any one of the sterols did not differ in volume, growth rate, contents of free sterol, esters and phospholipids, or phospholipid composition . Cholesterol-enriched cells contained about 2% more lipid than cells enriched in any of the other sterols, which was largely accounted for by increased contents of triacylglycerols and, to a lesser extent, esterified sterols . Phospholipids were enriched to the extent of about 52 to 63% with C18:1 residues . Cells enriched in ergosterol or stigmasterol were slightly less susceptible to the action of a wall-digesting basidiomycete glucanase than cells enriched with any one of the other sterols . The capacity of the plasma membrane to resist stretching, as indicated by the stability and volume of spheroplasts suspended in hypotonic solutions of buffered sorbitol (particularly in the range 0.9 to 0.7 M), was greater with spheroplasts enriched in sterols with an unsaturated side chain at C17 (ergosterol or stigmasterol) than with any of the other sterols . Plasma membranes were obtained from spheroplasts enriched in cholesterol or stigmasterol and had free sterol fractions containing 70 and 71%, respectively, of the sterol supplied exogenously to the cells . The sterol-phospholipid molar ratios in these membranes were, respectively, 1:7 and 1:8. J Bacteriol, 1976 Jul, 127(1), 610 - 8 Morphogenic effects of alpha-factor on Saccharomyces cerevisiae a cells; Lipke PN et al.; Saccharomyces cerevisiae mating type a cells enlarged and elongated when exposed to alpha-factor, a sex pheromone produced by mating-type alpha cells . This morphogensis required exogenous-D-glucose, nitrogen, and phosphate, and cells in exponential phase responded better than stationary-phase cells . Morphogenesis was blocked by cycloheximide and by inhibitors of cell wall biosynthesis such as 2-deoxy-D-glucose, 2-deoxy-2-fluoro-D-glucose, and 2-deoxy-2-fluoro-D-mannose, but not by polyoxin D . One to two hours after addition of pheromone, a cells became more susceptible to lysis by glucanases, a change that was dependendent on the dose of alpha-factor and was blocked by drugs that block morphogenesis . On the other hand, treatment with alpha-factor did not increase susceptibility to attack by trypsin, subtilisin, or exo-alpha-mannanase . Radioactive label, incorporated into cell wall polysaccharides during treatment with alpha-factor, was not secreted into the medium during morphogenesis . Analysis of the labeled wall polymers showed that alpha-factor-treated cells contain more glucan and less mannan than control cells, and that the mannan of treated cells contains an increased proportion of shorter side chains and unsubstituted backbone mannose units . Thin-section electron microscopy of treated cells revealed that the cell wall possesses a diffuse outer layer in the extension and is thinner at the tip. J Bacteriol, 1976 Jul, 127(1), 128 - 34 Influence of pH on the rate of ribosomal ribonucleic acid synthesis during sporulation in Saccharomyces cerevisiae; Wejksnora P et al.; The rate of synthesis of ribosomal RNA (rRNA) is much slower during sporulation than during vegetative growth of yeast . If sporulating cells are transferred from normal incubation conditions at pH 8.8 to the same medium adjusted to pH 7.0, the rate of rRNA synthesis increased to approach that observed in vegetative cells . The response to the pH change is quite rapid, occurring within 10 min . THE PH-dependent, rate-limiting step appears to be in the processing of 35S ribosomal precursor RNA to the final 26S and 18S RNA species . A similar pH effect also was found for the rate of protein synthesis . However, no change in respiration was observed when the pH was lowered . These results indicate that the observed differences in rate of rRNA synthesis in vegetative and sporulating cells are a consequence of pH and are not intrinsic to sporulation . The results also support the correlation between rRNA processing and protein synthesis. Mol Gen Genet, 1976 Jun 15, 145(3), 327 - 33 Cis-dominant regulatory mutations affecting the formation of glucose-repressible alcohol dehydrogenase (ADHII) in Saccharomyces cerevisiae; Ciriacy M; The formation of ADHII in Saccharomyces cerevisiae is regulated by carbon catabolite repression . There are two genes involved in the formation of ADHII: ADR2, the structural gene as identified by electrophoretic variants and ADR1, possibly a regulatory gene . A new genetic element involved in the regulation of ADHII was identified by three allelic mutants insensitive to strong glucose repression . They were called ADR3c (wild type designation ADR3) and found to be tightly linked to the structural gene, ADR2 . The alcohol dehydrogenase found in ADR3c mutants could not be distinguished electrophoretically from the ADHII of the glucose-sensitive wild type, ADR3 . Dominance relations between ADR3c and ADR3 were established in diploids heterozygous for ADR3 and the two alleles of ADR2 (ADR2-S: slow ADHII, ADR2-F: fast ADHII) . During growth on 10% glucose, an ADR3c adr2-F/ADR3 ADR2-Sheterozygous diploid formed only the fast ADHII variant wheras an ADR3c ADR2-S/ADR3 ADR2-F heterozygote produced only the slow form . This was taken as evidence of the cis-dominance of all ADR3c alleles . The cis-effect of ADR3c was also demonstrated in glucose-derepressed diploids . The ADR3c mutations do not only cause glucose-insensitive ADHII frmation, but also reduce the activity of the adjacent structural gene during derepression . Thus ADR3c alleles were considered to be controlling site mutations . No pleiotropic effects were observed on the formation of enzymes related to the function of ADHII . An adr1 ADR2 ADR3 single mutant did not form ADHII . In contrast to this, an adr1 ADR2 ADR3c double mutant formed ADHII at a similar level as double mutant formed ADHII at a similar level as an ADR1 ADR2 ADR3c mutant . This showed that ADR3c was epistatic over adr1 (previously suggested as a positive regulatory gene) . From this it was concluded that ADR1 is the fact a positive regulatory gene the function of which is required for the expression of the structural gene for ADHII, ADR2 . ADR3 is the controlling site for the structural gene ADR2 . Mutations at this site, ADR3c, alleviate the requirement for the ADR2 gene product . Adr3c is discussed as a promotor or operator site. Mol Gen Genet, 1976 Jun 15, 145(3), 287 - 91 Division delay and DNA degradation after mutagen treatment of the yeast, Saccharomyces cerevisiae; Wilmore PJ et al.; The treatment of the yeast mutant TMP1-1, which is capable of incorporating low levels of 3H-thymidine-5' - monophosphate with UV light and ethyl methane sulphonate resulted in division delay when cultures were reinnoculated into fresh medium . The initiation of cell division was accompanied by the degradation of up to 20% of the nuclear DNA fraction . The period of DNA degradation correlates closely with the time at which yeast cultures undergo mitotic recombination and appears to represent the degradation of DNA during a post-replication repair process. Mol Gen Genet, 1976 Jun 15, 145(3), 259 - 71 Fine structure of the URA2 locus in Saccharomyces cerevisiae . II . Meiotic and mitotic mapping studies; Denis-Duphil M et al.; The URA2 locus codes for a multifunctional enzyme complex carrying aspartate transcarbamylase (ATCase) and carbamyly phosphate synthetase (CPSase) activities . Three different types of ura2 mutants were tested in meiotic and mitotic recombination experiments: ura2A mutants devoid of ATCase activity, ura2C mutants devoid of CPSase activity and ura2B mutants devoid of both activities . All the ura2A mutations were found to be clustered at one end of the URA2 locus, called zone A, while the ura2C mutations were localized in a region at the other end, called zone C . All but two ura2B mutations (most of them suppressible) were distributed throughout zone C; the two ura2B exceptions which are small deletions, mapped in zone A . On the meiotic as well as on the mitotic map an intermediary or dead-space zone is located between zones A and C . No mutation has yet been found to map in this zone . The relative lengths of the three zones A, intermediary and C are 1 :2-3 :3-4, respectively . These data are consistent with the hypothesis that the URA2 locus consisting of at least two cistrons: C (CPSase) and A (ATCase), is transcribed into a single polycistronic message in the direction C to A . However, alternative hypotheses in reference to Peterson and MacLaughlin's observations (1973) are discussed. J Biol Chem, 1976 Jun 10, 251(11), 3367 - 74 The activating system of chitin synthetase from Saccharomyces cerevisiae . Purification and properties of the activating factor; Ulane RE et al.; The yeast proteinase that causes activation of the chitin synthetase zymogen has been purified by a procedure that includes affinity chromatography on an agarose column to which the proteinaceous inhibitor of the enzyme had been covalently attached . The purified enzyme yielded a single band upon disc gel electrophoresis at pH 4.5 in the presence of urea . At the same pH, but without urea, a faint band was detected in coincidence with enzymatic activity, whereas at pH 9.5, either in the absence or in the presence of sodium dodecyl sulfate, no protein zone could be seen . From sedimentation and gel filtration data, a molecular weight of 44,000 was estimated . The proteinase was active within a wide range of pH values, with an optimum between pH 6.5 AND 7 . Titraton of the activity with the protein inhibitor from yeast required 1 mol of inhibitor/mol of enzyme . A similar result was obtained with phenylmethylsulfonyl fluoride, an indication that 1 serine residue is required for enzymatic activity . The enzyme exhibited hydrolytic activity with several proteins and esterolytic activity with many synthetic substrates, including benzoylarginine ethyl ester and acetyltyrosine ethyl ester.A comparison of the properties of the enzyme with those of known yeast proteinases led to the conclusion that the chitin synthestase activating factor is identical with the enzyme previously designated as proteinase B (EC 3.4.22.9) . This is the first time that a homogeneous preparation of proteinase B has been obtained and characterized. Biochim Biophys Acta, 1976 Jun 2, 435(1), 21 - 9 A nonspecific inhibitory effect of tRNA on the activity of 3-deoxy-D-arabino-heptulosonate-7-phosphate synthase from Saccharomyces cerevisiae; Bell JB et al.; The inhibitory effect of tRNA on yeast 3-deoxy-D-arabino-heptulosonate-7-phosphate (DAHP) synthase (EC 4.1.2.15) has been reinvestigated . From earlier studies the inhibition by tRNAPhe appeared to be quite specific . This study shows that tRNAPhe is indeed a potent inhibitor but so is unfractionated tRNA, as well as ribosomal RNA and heparin . Complete digestion to mononucleotides relieves the inhibition . Since the enzyme requires a metal ion (Co2+) we suggest that the RNA and heparin are inhibitory by virtue of their capacity to chelate the Co2+. Proc Natl Acad Sci U S A, 1976 Jun, 73(6), 2072 - 6 Characterization of 2-mum DNA of Saccharomyces cerevisiae by restriction fragment analysis and integration in an Escherichia coli plasmid; Hollenberg CP et al.; Electrophoretic analysis of EcoRI and HindIII restriction fragments of 2-mum supercoiled DNA of Saccharomyces cerevisiae indicated that this class of DNA is heterogeneous and probably consists of two types of molecules . Integration of the 2-mum yeast DNA in E . coli plasmid pCR1 directly showed that existence of two types of molecules as each of these could be individually inserted into separate bacterial plasmids . The difference between the two types of 2-mum circles is due to an inversion of about 1.6 X 10(6) daltons . The inversion is flanked by a reversed duplicated sequence of 0.45 X 10(6) daltons . Possible implications of this structure are dicussed. Proc Natl Acad Sci U S A, 1976 Jun, 73(6), 2061 - 5 A chromosomal gene required for killer plasmid expression, mating, and spore maturation in Saccharomyces cerevisiae; Leibowitz MJ et al.; "Killer" strains of Saccharomyces cerevisiae are those that harbor a double-stranded RNA plasmid and secrete a toxin that kills only strains not carrying this plasmid (sensitives) . Two chromosomal genes (kex1 and kex2) are required for the secretion of toxin by plasmid-carrying strains . The kex2 gene, which maps at a site distinct from the mating-type locus, is also required for normal mating by alpha strains and meiotic sporulation in all strains . Strains that are alpha mating-type and kex2 fail to secrete the pheromone alpha-factor or to respond to the alpha-factor II pheromone which causes a morphological change, but they do respond to alpha-factor I which causes G1 arrest in alpha cells . Strains that are alpha mating-type and kex2 show no defect in mating; pheromone secretion, or response to alpha-factor . Diploids that are homozygous for the kex2 mutation, unlike wildtype or heterozygous diploids, fail to undergo sporulation, with the defect occurring in the final spore maturation stage . These same defects in the sexual cycle are present in all kex2 mutants independent of the presence of the "killer" plasmid. J Cell Sci, 1976 Jun, 21(1), 119 - 27 Subcellular localization of diffusible ions in the yeast Saccharomyces cerevisiae: quantitative microprobe analysis of thin freeze-dried sections; Roomans GM et al.; In yeast cells, of which the intracellular potassium had been partly replaced by rubidium or caesium, the intracellular ion distribution was studied by means of energy-dispersive X-ray microanalysis . The cells were rapidly frozen and thin sections were cut at low temperature on a cryo-ultramicrotome without the use of a trough liquid . By this dry cryosectioning procedure, complete retention of the diffusbile ions in the cells was obtained . Unless the sections had been exposed to moisture, no signs of redistribution were apparent . For quantitative determinations a gelatin standard, containing known amounts of the elements of interest, was prepared in the same way as the cells . The concentrations of potassium, rubidium, caesium and chloride in the nucleus, the cytoplasm and the vacuole could be measured . The intracellular distributions of potassium, rubidium and caesium were very similar . The concentrations of these ions in the cytoplasm were about equal to those in the nucleus and twice those in the vacuole . The total concentration in the cytoplasm was 180-190 mmol/kg fresh weight, in the nucleus 190-200 mmol/kg fresh weight and in the vacuole 75-90 mmol/kg fresh weight . The permeability of the yeast cell for chloride is markedly lower than for the cations. Arch Microbiol, 1976 Jun, 108(2), 211 - 5 Biosynthesis of sulphur amino acids in Saccharomyces cerevisiae II . Analysis of suplhite-producing strains; Romano P et al.; A number of strains of Saccharomyces which produce sulphite by sulphate reduction were examined from an enzymatic and genetic point of view . There are a number of mechanisms that regulate this activity . All of these mechanisms involve the sulphite-reducing activity . In the strains examined, reduced function as a result of mutation in the Sr-locus (affecting H2S-NADP oxidoreductase EC 1.8.1.2), repression of biosynthesis of the enzyme because of a mutation below the specific locus, and inhibition of the enzyme by endogenous factors were found to be responsible . The production of sulphite can also be connected with a complex state of heterozygosity . It is probably this multiplicity of biochemical and genetic mechanisms that accounts for the frequency with which the production of sulphite is observed in wild strains in nature. Arch Microbiol, 1976 Jun, 108(2), 149 - 52 Promotion of sporulation by caffeine pretreatment in Saccharomyces cerevisiae . II . Changes in ribonuclease activity during sporulation; Tsuboi M et al.; Changes in RNase activity during sporulation of a homothallic diploid strain of Saccharomyces cerevisiae were measured in caffeine-treated and non-treated cells . 1 . In caffeine-treated cells soon after the transfer to the sporulation medium a significant increase in RNase activity was observed; in control cells the rise of RNase activity was less and started after a lag period of 5 h . The final activity of RNase activity was about twice as high in caffeine-treated cells as in control cells . 2 . Increase in RNase activity during sporulation was sensitive to cycloheximide in control cells, but insensitive in caffeine-treated cells . 3 . RNases from vegetative cells and from sporulating ones are different in their Km values . Relation of the changes in RNase activity to premeiotic DNA synthesis is discussed. Can J Microbiol, 1976 Jun, 22(6), 873 - 83 Characterization of a temperature-sensitive mutant of Saccharomyces cerevisiae that undergoes uncontrolled protein synthesis; Gentile JM et al.; A mutant of Saccharomyces cerevisiae, DW137, isolated after treatment of a wild-type strain with ICR-170 . The mutant was respiration-deficient and showed abnormal cell division when grown at 30 degrees C . In addition, the mutant was temperature-sensitive and underwent lysis when grown at 37 degrees C . Random spore analysis, induced reversion profiles, and complementation analysis indicated that the abnormal phenotypes were under the control of a single recessive mutation caused by a base-pair substitution in a nuclear gene . Macromolecular analysis of the mutant at permissive and restrictive temperatures showed that at restrictive temperatures the mutant cannot synthesize DNA . Surprisingly, at restrictive temperatures, protein synthesis in the mutant continued at a rate greater than that observed at permissive temperatures . Cell death and lysis of the mutant could be prevented by treatment of cultures with cycloheximide, an inhibitor of protein synthesis . The data suggest that the abnormally high rate of protein synthesis and the inability to synthesize DNA are jointly responsible for death of the cells, and most probably play and integrating role in the incipient cell lysis. Eur J Biochem, 1976 May 17, 65(1), 257 - 62 Isolation and characterization of four related peptides exhibiting alpha factor activity from Saccharomyces cerevisiae; Stotzler D et al.; The molecular structure of alpha factor, a mating hormone produced by alpha mating type cells of Saccharomyces cerevisiae has been investigated . From culture filtrates of alpha cells four oligopeptides exhibiting alpha factor activity have been isolated . These peptides, designated as alpha1, alpha2, alpha3, and alpha4 are structurally closely related, being composed of thirteen (alpha1 and alpha3) and twelve (alpha2 and alpha4) amino acids, respectively . The peptides were found to be composed of the following amino acids: 2 glutamic acid or glutamine, 2 proline, 1 glycine, 1 methionine or methionine sulfoxide, 2 leucine, 1 tyrosine, 1 lysine, 1 histidine, 1 or 2 tryptophan . The tridekapeptides differ from the dodekapeptides by an additional NH2-terminal tryptophan residue . Tyrosine was identified as the C-terminal amino acid in all four peptides . alpha3 and alpha4 are oxidation products containing an internal methionine sulfoxide instead of methionine . The mechanisms which could introduce the observed heterogeneity of the peptides are discussed. Arch Microbiol, 1976 May 3, 108(1), 27 - 33 Mating reaction in Saccharomyces cerevisiae . IX . Regulation of sexual cell agglutinability of a type cells by a sex factor produced by alpha type cells; Shimoda C et al.; A diffusible sex-specific substance called alpha substance-I (alphaS-I) was isolated from culture filtrate of alpha type strains of the yeast Saccharomyces cerevisiae . The isolated alphaS-I, an oligopeptide, induced sexual cell agglutinability in inducible alpha type strains and enhanced the agglutinability in constitutive a type strains . The induction of sexual agglutinability was detected in 30 min and reached maximum in 90 min, when 0.2 mug/ml of alphaS-I was added to inducible a type cells . The a type-specific factor responsible for sexual cell agglutination, called a type agglutination factor (aAF), was shown to be produced during the induction or the enhancement of agglutinability of a type cells by alphaS-I . The aAF produced in response to alphaS-I was not different in the susceptibility to proteolytic enzymes and disulfide-cleaving agents from those produced constitutively in the absence of alphaS-I. Z Naturforsch {C}, 1976 May-Jun, 31(5-6), 298 - 303 {Effect of N-methyl-N-beta-chloroethylhydrazine and its benzaldehydhydrazone on RNA-and protein synthesis as well as metabolism of synchronously growing yeast cells (Saccharomyces cerevisiae) (author's transl)}; Braun R et al.; N-methyl-N-beta-chloroethylhydrazine and its benzaldehydhydrazone inhibit the influx of {6-3H}-uracil and L-{U-14C}leucin in yeast cells as well as the incorporation in RNA and protein . Experiments with synchronously and asynchronously growing cells showed the N-methyl-N-beta-chloroethylhydrazine essentially influences the dividing phase while the benzaldehydhydrazone is more effective in the growth phase . The effect of these two substances on respiration, glycolysis and the concentration of fructose-1,6-diphosphate, triose phosphate, and adenosine triphosphate is small. Z Naturforsch {C}, 1976 May-Jun, 31(5-6), 292 - 7 {Effect of N-methyl-N-beta-chloroethyl-hydrazine-HCl on the growth and multiplication of yeast cells (Saccharomyces cerevisiae) (author's transl)}; Braun R et al.; N-Methyl-N-beta-chloroethyl-hydrazine-HCl and its benzaldehydhydrazone inhibit growth and multiplication of yeast cells . The DNA-synthesis is partially blocked . After removal of the substances the rate of this synthesis is much more increased than that of RNA and protein . The both substances we tested are more effective than simple alkylhydrazines. Can J Microbiol, 1976 May, 22(5), 762 - 4 Regulation of acetyl-CoA synthetase of Saccharomyces cerevisiae; Coleman JS et al.; Acetyl-coenzyme A synthetase (EC 6.2.1.1) activity of Saccharomyces cerevisiae was determined by a radioactive assay procedure . The activity in vitro was inhibited significantly by NADPH, NADH, or AMP and to a lesser extent by NADP, NAD, or ADP . Glutamic acid and alpha-ketoglutaric acid were not inhibitory . The enzyme level was repressed when the cells were grown in a complex nutrient medium as opposed to the minimal medium . However, a glutamic acid auxotroph glul, when grown in excess glutamic acid, demonstrated a fivefold increase of acetyl-CoA synthetase. J Bacteriol, 1976 May, 126(2), 661 - 7 Ribonucleic acid synthesized in meiotic cells of Saccharomyces cerevisiae: effect of culture medium pH; Curiale MS et al.; Pulse-labeled ribonucleic acid (RNA) was extracted from polysomes of sporulating cells of Saccharomyces cerevisiae and characterized in sucrose gradients and by sodium dodecyl sulfate-polyacrylamide gel electrophoresis . Transfer RNA, ribosomal RNA, and heterodisperse RNA, presumed to be messenger RNA, were synthesized during a 20-min pulse at T4 and T6 when labeling was performed in sporulation medium adjusted to pH 6.0 . Furthermore, ribosomal RNA was processed into functional ribosomes during the pulse . The specific activity of pulse-labeled RNA of cells labeled in sporulation medium where the pH was unadjusted at T4 (pH 7.8) and T9 (pH 8.6) was 20- to 50-fold lower than RNA from cells labeled at pH 6.0 . The low specific activity resulted from a 50-fold reduction in uptake of labeled precursors when the medium pH was greater than 7.2 . However, heterodisperse RNA ranging from 4-17S in size and transfer RNA were synthesized during the pulse at T4 (pH 7.8),but the low specific activity of ribosomal RNA prevented a thorough analysis of its synthesis . Cellular impermeability at T9 (pH 8.6) resulted in minimal uptake of label, and an analysis of pulse-labeled transcripts was impossible . A comparison of the percantage of polysomal material indicate, however, that these cells were at least as active in translation as cells pulse-labeled at pH 6.0. Genetics, 1976 Apr, 82(4), 645 - 63 Genetic analysis of petite mutants of Saccharomyces cerevisiae: transmissional types; Perlman PS; We have studied a number of petite {rho-} mutants of Saccharomyces cerevisiae induced in a wild-type strain of mitochondrial genotype {ome- CHL(R) ERY(S) OLI(S) (1, 2, 3) PAR(S)} by Berenil and ethidium bromide, all of which have retained two mitochondrial genetic markers, {CHL(R)} and {ERY(S)}, but have lost all other known markers . Though stable in their ability to retain these markers in their genome, these mutants vary widely among themselves in suppressiveness and in the extent to which the markers are transmitted on crossing to a common wild-type tested strain . In appropriate crosses all of the strains examined in this study demonstrate mitochondrial polarity, and thus have also retained the {ome-} locus in a functional form; however, five different transmissional types were obtained, several of them quite unusual, particularly among the strains originally induced by Berenil . One of the most interesting types is the one that appears to reverse the parental genotypes with {CHL(R) ERY(S)} predominating over {CHL(S) ERY(R)} in the diploid {rho+} progeny, rather than the reverse, which is characteristic of analogous crosses with {rho+} or other petites . Mutants in this class also exhibited low or no suppressiveness . Since all of the petites reported here are derived from the same wild-type parent, and so have the same nuclear background, we have interpreted the transmissional differences as being due to different intramolecular arrangements of largely common retained sequences. Genetics, 1976 Apr, 82(4), 639 - 44 Mutants of Saccharomyces cerevisiae resistant to the alpha mating-type factor; Manney TR et al.; Mutants that are resistant to alpha-factor have been isolated from a mating-type haploid strains of yeast by direct selection on agar medium containing partially purified alpha-factor . All resistant mutants isolated were found to be sterile . They were characterized and compared with mutants previously isolated as non-mating . Among 93 able to mate at low frequency and to sporulate, none showed linkage to the mating-type locus . The results support the hypothesis that the response to alpha-factor by cells of mating-type a is essential for mating. Biotechnol Bioeng, 1976 Apr, 18(4), 449 - 63 Influence of salts and gelatin on disintegration of Saccharomyces cerevisiae by freeze-pressing; Magnusson KE et al.; The disintegration by freeze-pressing of a low concentration of Saccharomyces cerevisiae suspended in aqueous solutions of gelatin and different salts has been studied at different temperatures . In the freeze-pressing process deionized water and salt solutions flow in pulses, whereas samples with increasing concentrations of gelatin or cells tend to flow more smoothly . This smooth flow enhances the disruption efficiency particularly at lower temperatures, which seems to be of great practical importance . The addition of salts also promotes disintegration . The presence of both gelatin and salts works antagonistically on disintegration presumably because of different modes of action at disruption of cells. J Bacteriol, 1976 Apr, 126(1), 243 - 50 Control of inositol biosynthesis in Saccharomyces cerevisiae; inositol-phosphate synthetase mutants; Culbertson MR et al.; Inositol-requiring mutants of Saacharomyces cerevisiae were tested in cell extracts for the ability to convert glucose-6-phosphate to inositol-phosphate (IP synthetase) and inositol (IP phosphatase) . Mutants representing any one of 10 unlinked loci conferring the inositol requirement were unable to synthesize either compound in an assay with glucose-6-phosphate as the substrate . These results indicate that the mutants lack IP synthetase activity and that at least 10 genes control the conversion of glucose-6-phosphate to inositol-phosphate . In addition, a mutation known to be unlinked with the ino1 locus interacts with a leaky ino1 allele and may play a role in the regulation of IP synthetase . This mutation causes a 47% reduction in wild-type IP synthetase activity and, when combined in a haploid strain with the leaky ino1 allele, it reduced IP synthetase activity to a level below that which is growth supporting . Wild-type and IP synthetase-deficient strains were tested for reduced nicotinamide adenine dinucleotide (NADH) accumulation, since NAD+ is required in the conversion of glucose-6-phosphate to inositol . No detectable accumulation of NADH was observed in the wild-type strain, presumably because the NADH generated is rapidly oxidized during subsequent partial reactions of IP synthetase . Mutants representing three different loci accumulate NADH and may, therefore, lack the NADH-mediated reductase activity of IP synthetase . Other mutants tested fail to accumulate NADH and may, therefore, lack the NAD+-mediated oxidase activity of IP synthetase . Phospholipid synthesis was studied by 32P pulse labeling in one mutant under conditions of inositol supplementation and starvation . Starved cells incorporate 32P into phospholipids normally for 2 h, followed by a period in which the rate of phosphatidylinositol synthesis decreases and the rate of phosphatidylcholine synthesis increases . After 5 to 6 h starvation, all cellular phospholipid synthesis ceases. J Bioenerg, 1976 Apr, 8(2), 93 - 107 Genetic analysis of mitochondrial biogenesis and function in Saccharomyces cerevisiae; Michaelis G et al.; Different mitochondrial mutants have been isolated that affect mitochondrial ribosome function . These mutants were used to establish most of the known methods and principles of mitochondrial genetics in yeast . Another class of mitochondrial mutants have been shown to affect mitochondrial ATPase and, more specifically, the "membrane factor" of mitochondrial ATPase . These mutants might be very useful in studying the energy-conserving function, and the interaction between the hydrophobic and hydrophylic parts, of the ATPase complex . New types of mitochondrial point mutations, concerning cytochrome a-a3 or b, will soon open up new fields of investigation . The biochemical and genetic analysis of numerous mutants belonging to that category and recently obtained {31} is being currently pursued in Tzagoloff's and Slonimski's laboratories. Mol Gen Genet, 1976 Mar 30, 144(3), 301 - 6 Macromolecule synthesis in a mutant of Saccharomyces cerevisiae inhibited by S-adenosyimethionine; Lipinski C et al.; Saccharomyces cerevisiae strain 83384-B3 carries the sai-1 mutation which confers sensitivity to S-adenosylmethionine (SAM) and S-adenosylhomocysteine (SAH) . It was shown that the mutant is impermeable to precursors of ribonucleic acid (RNA) and protein during inhibition by SAM (0.2 mM) . Inhibition of uptake of adenine and uracil was nearly complete 3 h after growth in the presence of SAM and the uptake of leucine was at least 10-fold lower . The incorporation of 3H-adenine into ribosomal RNA, transfer RNA and heterodisperse RNA, believed to be messenger, was reduced 10-fold when measured after 1 h inhibition . The inhibition of growth was completely reversed by methionine (2.0 mM) in cells previously exposed to SAM for 90 min . The polysome content in cells inhibited by SAM was 25% less than the control after 4 h inhibition . Ribosome synthesis increased only about 40% in the presence of SAM and about 5-fold in the control over an 8 h period . All classes of RNA were synthesized during inhibition. Mol Gen Genet, 1976 Mar 30, 144(3), 289 - 99 Cytoplasmic inheritance in Saccharomyces cerevisiae: comparison of zygotic mitochondrial inheritance patterns; Aufderheide KJ et al.; Mitochondrial movements in Saccharomyces cerevisiae (Sc) zygotes were monitored with phase-contrast microscopy and compared to known mitochondrial inheritance systems . The mitochondria of Sc were convincingly identified by integrated use of phase-contrast, cytochemical and electron microscopic observations . Mitochondria in Sc appear to move by saltatory jumps, which appear to be oriented towards movement of mitochondria into developing buds . Tracking of mitochondria of different genotypes was made possible by positive identification of each mitochondrial population before zygosis, and by the low degree of mixing (less than 10%) of mitochondrial populations before first bud septation . A grande by grande cross demonstrated equal numbers of mitochondria from each haploid moving into the first zygotic bud . A grande by neutral petite cross gave a 2:1 ratio of grande to petite mitochondria . However, a grande by suppressive petite cross gave equal numbers of grande and petite mitochondria . Using drug resistance systems, a comparison was made of highly biased (97%) and moderately biased (71%) chloramphenicol resistant inheritance patterns . In both cases, the ratios of drug resistant to sensitive mitochondria were 1:1 . When numbers of mitochondria moving into an individual bud were compared to the phenotypic content of the clone of that bud, no model could be constructed which could predict the latter from the former . The data indicate (with the exception of the neutral petite by grande cross) that the numbers of each mitochondrial type "inserted" into the first zygotic bud are equal, regardless of the degree of asymmetry of inheritance of mitochondrial markers. Mol Gen Genet, 1976 Mar 30, 144(3), 281 - 8 Some physiological alteration associated with pleiotropic cross resistance and collateral sensitivity in Saccharomyces cerevisiae; Rank GH et al.; A mutant strain (2-20) isolated by growth on medium containing oligomycin and cycloheximide was also found to be cross resistant to antimyicn, cerulenin, chloramphenicol, tetracycline, triethyltin and triphenylmethylphosphonium bromide, but collaterally sensitive to dequalinium chloride, gentamycin, neomycin, paromomycin and thiolutin . Growth of 2-20, compared to the parental strain and 2 complete revertants, under a variety of environmental conditions revealed that strain 2-20 had an enhanced sensitivity to increased osmolality, elevated pH, and high temperature; in addition, strain 2-20 was unable to polymerize aminoimidazole ribotide at 37 degrees C as shown by the failure to develop a red colony in the presence of ade 2 . Four complex solid media (glucose--KCI, galactose, ethanol, ethanol--KCI, Table 1) unable to sustain the growth of strain 2-20 were arbitrarily chosen to monitor cellular growth under different physiological conditions . Tetrad analysis indicated that the complex phenotype (cross resistance, collateral sensitivity, inablity to polymerize aminoimidazole ribotide, absence of growth under adverse physiological conditions) was inherited by an allele of a locus previously shown to result in a permeability barrier of the plasma membrane to chloramphenicol . 582 of 640 subclones used to isolate revertants of 2-20, under four different physiological conditions, were observed to produce a complete revertant of the complex phenotype . It is proposed that the pleiotropic phenotype could result from an alteration of the plasma membrane and mitochondrial inner membrane by a single nuclear gene mutation. Genetics, 1976 Mar 25, 82(3), 429 - 42 Two chromosomal genes required for killing expression in killer strains of Saccharomyces cerevisiae; Wickner RB et al.; The killer character of yeast is determined by a 1.4 X 10(6) molecular weight double-stranded RNA plasmid and at least 12 chromosomal genes . Wild-type strains of yeast that carry this plasmid (killers) secret a toxin which is lethal only to strains not carrying this plasmid (sensitives).--We have isolated 28 independent recessive chromosomal mutants of a killer strain that have lost the ability to secrete an active toxin but remain resistant to the effects of the toxin and continue to carry the complete cytoplasmic killer genome . These mutants define two complementation groups, kex1 and kex2 . Kex1 is located on chromosome VII between ade5 and lys5 . Kex2 is located on chromosome XIV, but it does not show meiotic linkage to any gene previously located on this chromosome.--When the killer plasmid of kex1 or kex2 strains is eliminated by curing with heat or cycloheximide, the strains become sensitive to killing . The mutant phenotype reappears among the meiotic segregants in a cross with a normal killer . Thus, the kex phenotype does not require an alteration of the killer plasmid.--Kex1 and kex2 strains each contain near-normal levels of the 1.4 x 10(6) molecular weight double-stranded RNA, whose presence is correlated with the presence of the killer genome. Biochim Biophys Acta, 1976 Mar 25, 428(1), 182 - 92 A gene controlling the synthesis of non specific alkaline phosphatase in Saccharomyces cerevisiae; Toh-E A et al.; Recessive mutants defective in the formation of non-specific alkaline phosphatase (EC 3.1.3.1) could be selected by staining colonies on a plate with p-nitrophenylphosphate after treatment with chloroform vapour . Since no complementation was observed among the nine mutants so far tested, all the mutations might occur in the same locus, phoH . The non-specific alkaline phosphatase was repressible, although a significant basal level of the enzyme activity was observed in the repressed condition. J Biol Chem, 1976 Mar 25, 251(6), 1799 - 807 The ribosomal proteins of Saccharomyces cerevisiae . Phosphorylated and exchangeable proteins; Zinker S et al.; Sixty-seven ribosomal proteins of the yeast Saccharomyces cerevisiae have been distinguished by two-dimensional polyacrylamide gel electrophoresis . Five of the ribosomal proteins are phosphorylated in vivo . One of the phosphorylated proteins appears to correspond to the phosphorylated ribosomal protein, S6, of rat liver . Another of the yeast-phosphorylated proteins, which is highly acidic, may be related to the protein L7/L12 of Escherichia coli . The phosphorylation of four of the five ribosomal proteins depends on protein synthesis . Ribosome synthesis, however, is not necessary for the phosphorylation of any of them . Three proteins of the 60 S ribosomal subunit are "exchangeable" in vivo . Two of these are phosphoproteins, one of which is the very acidic protein possibly related to L7/L12 of E . coli . The possible significance of this phosphorylated, exchangeable protein in protein synthesis is discussed. Mol Gen Genet, 1976 Mar 22, 144(2), 213 - 5 Mutational properties of supP amber-ochre supersuppressors in Saccharomyces cerevisiae; Gerlach WL; Mutational properties of the supP amber-ochre supersuppressor locus in Saccharomyces cerevisiae are described . They are consistent with the proposition that the supP locus encodes a protein. Mol Gen Genet, 1976 Mar 22, 144(2), 131 - 40 The effect of dose and time on the induction of genetic alterations in Saccharomyces cerevisiae by aminoacridines in the presence and absence of visible light irradiation in comparison with the dose-effect-curves of mutagens with other type of action; Fahrig R; Aminoacridines induce frameshift mutations and are photodynamically active, depending on whether visible light is absent or present . Therefore, a test system which allows to compare quantitatively the genetic effects of aminoacridines irradiated or unirradiated by visible light ought to be susceptible to the different DNA alterations which can be induced by these substances . For this reason in most experiments mitotic gene conversion and only in some selected experiments reverse mutation was chosen as the indicator of genetic activity . In contrast to mutation systems mitotic gene conversion has never shown a response specific to only some types of mutagens . The three aminoacridine derivatives used-acridine orange (AO), proflavine (PF), and acridine yellow (AY)-were successful in the induction of convertants at two different loci . No locus-specificity could be observed . The time-dependent induction of convertants proceeds quickly but soon reaches-especially after treatment without light-a saturation point . The dose/effect-curve after treatment in the dark has a slope increasing with increasing concentration . Irradiation with visible light results in a dose/effect-curve consisting of three parts . Af first the increase of convertants is nearly linear extending one (AY) to three (AO) orders of magnitude . After a saturation effect begins at the point at which an effectiveness of the acridines in the dark is apparent . At high concentrations an induction of convertants can again be observed which is nearly the same as that after treatment in the dark . To determine whether the dose/effect-curves obtained for gene conversion refer to similar curves for gene mutations after treatment with AO at the same locus not only gene conversions but also reverse mutations were scored for . AO-treatment in the dark is ineffective in inducing reverse mutations . Irradiation with visible light results in a dose/effect-curve beeing parallel only in its first part to the dose/effect-curve obtained for gene conversion, while in its second part a mutation frequency decline can be observed . Comparing the dose/effect-curves of AO resulting from the induction of gene conversion and gene mutation, and taking into account that no mutants can be induced by AO-treatment in the dark, the increase in convertants at high acridine-concentrations can be explained as an addition of light-dependent and light-independent effects . That means, in mutation systems at low concentrations of aminoacridines irradiation with visible light should cause transitions, transversions and microlesions, at intermediate concentrations frameshift lesions should begin to appear, and at very high concentrations nearly exclusively frameshift lesions should occur . The dose/effect-curves of aminoacridines compared with those of other mutagens are very complex . The dose/effect-curves of the mutagens of other type of action tested are linear in a double logarithmic scale, and parallel for induced gene conversion and induced gene mutation... Arch Microbiol, 1976 Mar 19, 107(2), 207 - 14 Free tryptophan pool and tryptophan biosynthetic enzymes in Saccharomyces cerevisiae; Fantes PA et al.; The free tryptophan pool and the levels of two enzymes of tryptophan biosynthesis (anthranilate synthase and indoleglycerolphosphate synthase)have been determined in a wild type strain of Saccharomyces cerevisiae and in mutants with altered regulatory properties. C R Acad Sci Hebd Seances Acad Sci D, 1976 Mar 15, 282(11), 1141 - 3 {Genetic effects of the gaseous phase of cigarette smoke on Saccharomyces cerevisiae}; Izard C et al.; The gaseous phase of cigarette smoke is active on Saccharomyces cerevisiae . A toxic effect and several genetic alterations were observed . Mitotic segregants are induced and the cytoplasmic "petite" mutation is selected and induced . These effects vary according to the growth phase of the culture and to the brand of cigarettes tested . Stationary phase cells are more resistant than exponentially growing ones. Biochem J, 1976 Mar 15, 154(3), 751 - 63 Distribution of membranes, especially of plasma-membrane fragments, during zonal centrifugations of homogenates from glucose-repressed Saccharomyces Cerevisiae; Nurminen T et al.; 1 . The distributions of several enzymes and other marker components were examined after zonal centrifugations of whole homogenates from glucose-repressed Saccharomyces cerevisiae on sucrose and iso-osmotic Ficoll, and the composition and morphology of the fractions were investigated . 2 . After high-speed zonal centrifugation most of the protein, acid and alkaline phosphatases, alkaline pyrophosphatase, adenosine monophosphatase, beta-fructofuranosidase, alpha-mannosidase, NADPH-cytochrome c oxidoreductase and an appreciable amount of phospholipid and sterol were non-sedimentable, i.e . were at densities below 1.09 (g/cm3) . Most of the RNA was at p=1.06-1.08 in Ficoll and at p=1.09-1.11 in sucrose . 3 . The bulk of the Mg2+-dependent adenosine triphosphatase (Mg-ATPase) was coincident with the main peak of phospholipid and sterol, at median density 1.10, which was also rich in smooth-membrane vesicles . In Ficoll, a minor peak of phospholipid and sterol at p-1.12-1.15 contained a smaller part of the oligomycin-insensitive Mg-ATPase and heavy membrane fragments . In sucrose, several minor peaks of Mg-ATPase were in the mitochondrial density range, and a peak of oligomycin-insensitive Mg-ATPase coincident with a minor peak of phospholipid and sterol at around p-1.25 contained heavy membrane fragments of high carbohydrate content, especially mannose . 4 . Further purification of the oligomycin-insensitive Mg-ATPase containing membrane preparations was performed on Urografin gradients . 5 . It is argued that the oligomycin-insensitive Mg-ATPase containing membranes are fragments of the plasma membrane, but have different densities because they contain different amounts of glycoprotein particles. J Bacteriol, 1976 Mar, 125(3), 999 - 1004 Utilization of D-asparagine by Saccharomyces cerevisiae; Dunlop PC et al.; Yeast strains sigma1278b and Harden and Young, which synthesize only an internal constitutive form of L-asparaginase, do not grow on D-asparagine, as a sole source of nitrogen, and whole cell suspensions of these strains do not hydrolyze D-asparagine . Strains X2180-A2 and D273-10B, which possess an externally active form of asparaginase, are able to grow slowly on D-asparagine, and nitrogen-starved suspensions of these strains exhibit high activity toward the D-isomer . Nitrogen starvation of strain X218O-A2 results in coordinate increase of D- and L-asparaginase activity; the specific activity observed for the D-isomer is approximately 20% greater than that observed for the L-isomer . It was observed, in studies with cell extracts, that hydrolysis of D-asparagine occurred only with extracts from nitrogen-starved cells of strains that synthesize the external form of asparaginase . Furthermore, the activity of the extracts toward the D-isomer was always higher than that observed with the L-isomer . A 400-fold purified preparation of external asparaginase from Saccharomyces cerevisiae X218U-A2 hydrolyzed D-asparagine with an apparent Km of 0.23 mM and a Vmax of 38.7 mumol/min per mg of protein . D-Asparagine was a competitive inhibitor of L-asparagine hydrolysis and the Ki determined for this inhibition was approximately equal to its Km . These data suggest that D-asparagine is a good substrate for the external yeast asparaginase but is a poor substrate for the internal enzyme. J Bacteriol, 1976 Mar, 125(3), 887 - 91 Kinetics of labeling of the S-adenosylmethionine pool of Saccharomyces cerevisiae; Warner JR et al.; A method has been developed for studying the specific activity of the pool of S-adenosylmethionine in yeast . The pool reaches half-maximal specific activity within 30 s after the addition of {methyl-3H}methionine . After addition of an excess of nonradioactive methionine, the specific activity of S-adenosylmethionine is reduced by half within 20 s . During that period there is a substantial expansion of the pool . A logarithmically growing cell in synthetic medium contains about 2 X 10(6) molecules of S-adenosylmethionine, of which only 10% is used for the methylation of ribonucleic acid molecules. J Bacteriol, 1976 Mar, 125(3), 864 - 71 Regulation of lysine transport by feedback inhibition in Saccharomyces cerevisiae; Morrison CE et al.; A steady-state level of about 240 nmol/mg (dry wt) occurs during lysine transport in Saccharomyces cerevisiae . No subsequent efflux of the accumulated amino acid was detected . Two transport systems mediate lysine transport, a high-affinity, lysine-specific system and an arginine-lysine system for which lysine exhibits a lower affinity . Preloading with lysine, arginine, glutamic acid, or aspartic acid inhibited lysine transport activity; preloading with glutamine, glycine, methionine, phenylalanine, or valine had little effect; however, preloading with histidine stimulated lysine transport activity . These preloading effects correlated with fluctuations in the intracellular lysine and/or arginine pool: lysine transport activity was inhibited when increases in the lysine and/or arginine pool occurred and was stimulated when decreases in the lysine and/or arginine pool occurred . After addition of lysine to a growing culture, lysine transport activity was inhibited more than threefold in one-third of the doubling time of the culture . These results indicate that the lysine-specific and arginine-lysine transport systems are regulated by feedback inhibition that may be mediated by intracellular lysine and arginine. J Bacteriol, 1976 Mar, 125(3), 1048 - 56 Urea transport-defective strains of Saccharomyces cerevisiae; Sumrada R et al.; Experiments characterizing the urea active transport system in Saccharomyces cerevisiae indicate that (i) formamide and acetamide are strong competitive inhibitors of urea accumulation, (ii) uptake is maximal at pH 3.3 and is 80% inhibited at pH 6.0, and (iii) adenosine 5'-triphosphate generated by glycolysis in conjunction with formation of an ion gradient is likely the driving force behind urea transport . Mutant strains were isolated that are unable to accumulate urea at external concentrations of 0.25 mM . These strains also exhibit a depressed growth rate on 10 mM urea, indicating existence of a relationship between the active transport and facilitated diffusion modes of urea uptake. J Bacteriol, 1976 Feb, 125(2), 595 - 600 Turnover of polyadenylate-containing ribonucleic acid in Saccharomyces cerevisiae; Hynes NE et al.; We examined the kinetics of incorporation of {3H}adenine into polyadenylate-containing ribonucleic acid {poly(A)-containing RNA} in yeast . The total poly(A)-containing RNA from spheroplasts and intact cells and the polysomal poly(A)-containing RNA exhibited similar incorporation kinetics . At 30 C half-saturation of the pool of poly(A)-containing RNA with label occurred in approximately 22 min . Since precursor pools appeared to require 5 min to saturate with label, we conclude that at 30 C messenger RNA molecules in yeast decay with an average half-life of 17 min. Genetics, 1976 Feb, 82(2), 273 - 85 Mutants of the killer plasmid of Saccharomyces cerevisiae dependent on chromosomal diploidy for expression and maintenance; Wickner RB; Mutants of the killer plasmid of Saccharomyces cerevisiae have been isolated that depend upon chromosomal diploidy for the expression of plasmid functions and for replication or maintenance of the plasmid itself . These mutants are not defective in any chromosomal gene needed for expression or replication of the killer plasmid.--Haploids carrying these mutant plasmids (called d for diploid-depen;ent) are either unable to kill or unable to resist being killed or both and show frequent loss of the plasmid . The wild-type phenotype (K+R+) is restored by mating the d plasmid-carrying strain with either (a) a wild-type sensitive strain which apparently has no killer plasmid; (b) a strain which has been cured of the killer plasmid by growth at elevated temperature; (c) a strain which has been cured of the plasmid by growth in the presence of cycloheximide; (d) a strain which has lost the plasmid because it carries a mutation in a chromosomal mak gene; or (e) a strain of the opposite mating type which carries the same d plasmid and has the same defective phenotype, indicating that the restoration of the normal phenotype is not due to recombination between plasmid genomes or complementation of plasmid or chromosomal genes.--Sporulation of the phenotypically K+R+ diploids formed in matings between d and wild-type nonkiller strains yields tetrads, all four of whose haploid spores are defective for killing or resistance or maintenance of the plasmid or a combination of these . Every defective phenotype may be found among the segregants of a single diploid clone carrying a d plasmid . These defective segregants resume the normal killer phenotype in the diploids formed when a second round of mating is performed, and the segregants from a second round of meiosis and sporulation are again defective. Nucleic Acids Res, 1976 Feb, 3(2), 465 - 76 Comparison of the fine structure of mitochondrial DNA from Saccharomyces cerevisiae and S . carlsbergensis: electron microscopy of partially denatured molecules; Christiansen G et al.; Denaturation-maps of mitochondrial DNA from Saccharomyces cerevisiae and S . carlsbergensis have been derived from electron microscopic observations of partially denatured complete circular molecules and large fragments of these circles . The mitochondrial DNA from the two species differ by 6% in total length, but seems from the maps to contain some regions of apparent close homology . The cleavage pattern of the two DNAs by the restriction endonuclease EcoRI is compared by gel electrophoresis. J Virol, 1976 Feb, 17(2), 472 - 6 Virus-like particles from killer, neutral, and sensitive strains of Saccharomyces cerevisiae; Adler J et al.; Procedures were developed for purification of virus-like particles (VLPs) from killer, neutral, and sensitive strains of Saccharomyces cerevisiae . Morphologically similar spherical VLPs measuring 40 nm in diameter were extracted from all three phenotypes . The particles were partially purified by high-speed centrifugation through a layer of CsCl (1.26 g/cm3) and sucrose density gradient centrifugation . Gradient-purified preparations contained three centrifugal species that sedimented at approximately 43, 102, and 162S . The 43S component is considered to be an artifact . Preparations from killer strains contained three double-stranded RNA (ds-RNA) components with molecular weights of 1.19 x 10(6), 1.29 x 10(6) and 2.54 x 10(6) . VLPs from neutral and sensitive strains contained only the largest ds-RNA species . VLP preparations were subsequently separated into two major density components by CsCl equilibrium gradient centrifugation . The light component banding at 1.28 to 1.30 g/cm3 was void of nucleic acid, and the heavy component banding at 1.40 g/cm3 contained only the largest ds-RNA species. Mutat Res, 1976 Feb, 34(2), 201 - 16 Induction of mitotic recombination with N-methyl-N'-nitro-N-nitrosoguanidine (MNNG) in Saccharomyces cerevisiae . A comparison between treatment in vitro and in the host-mediated assay; Ryttman H et al.; Two methods, treatment in vitro and the host-mediated assay method, were compared in their ability to demonstrate the induction of MNNG of nitotic recombination in a diploid strain of Saccharomyces cerevisiae . MNNG had a strong activity in vitro but not in the host-mediated assay at the concentrations tested . When the genetic effects of MNNG have been tested in different test systems, sometimes negative, sometimes positive results have been obtained . The relevance of different tests for risk evaluation is discussed, and it is concluded from the data on MNNG that tests on whole mammals may sometimes give false negative results because the cells tested are, in parts of the body, less accessible to the mutagen . Increasing doses of MNNG by treatment in vitro gave decreasing frequencies of mitotic recombination, indicating damage to the recombinational system in the cells . Dose-response relationships for recombination and mutation are discussed. Arch Microbiol, 1976 Feb, 107(1), 63 - 70 The intramitochondrial location of cytochrome c peroxidase in wild-type and petite Saccharomyces cerevisiae; Williams PG et al.; Cytochemical and ultrastructural analysis of wild-type cells of Saccharomyces cerevisiae, grown aerobically in a glucose-limited chemostat, shows that cytochrome c peroxidase is localized between the membranes of the cristae, that is, in the intracristal space . This enzyme is thus positioned appropriately within the organelle to act as an alternate terminal oxidase for the respiratory chain . The proximity of the peroxidase to major sites of generation of its two substrates may account for the small leakage of hydrogen peroxide from yeast mitochondria, as compared with the larger outflow from mammalian mitochondria . In the cytoplasmic petite mutant, gross distortion of promitochondrial membrane arrangement is evident . Nevertheless, cytochrome c perioxidase activity is present in the same amounts as is found in wild-type cells, and is localized predominantly within annuli of membrane which constitute the promitochondria in these cells . No unequivocal evidence was obtained for the localization of catalase in microbodies or other organelles in either wild-type or petite cells. Mol Gen Genet, 1976 Jan 16, 143(2), 131 - 65 Mitochondrial genetics . XI . Mutations at the mitochondrial locus omega affecting the recombination of mitochondrial genes in Saccharomyces cerevisiae; Dujon B et al.; 1 . A series of CS revertants has been selected from various strains (both omega+ and omega-) carrying a CR mitochondrial mutation at the RIB1 locus . The properties of mitochondrial recombination exhibited by these CS revertants in various crosses, have been examined systematically . The omega allele of the CS revertants has been defined in crosses with omega+ and omega- tester strains using two criteria: the polarity of recombination and a new criterium called relative output coefficient . We found that mutations of omega appear frequently associated with the mutations at the RIB1 locus selected from omega- strains but not with those selected from omega+ strains . A new allelic form of omega (omega n) which had not been found amongst wild type yeast strains is characterised . Similarly omega n mutation was found frequently associated with CR mutants at the RIB1 locus selected from omega- CS strains but not with those selected from omega+ CS strains . The omega n mutants, and the omega+ and omega- strains, explain the groups of polarity previously observed by Coen et al . (1970) . 2 . Main features of mitochondrial crosses with omega n strains (omega+ x omega n, omega- x omega n and omega n x omega n) are analysed . Recombination is possible between the different mitochondrial genetic markers . No high polarity of recombination is observed and the frequency of recombinants are similar to those found in homosexual crosses (omega+ x omega+ and omega- x omega-) . A striking property, observed for the first time, exists in crosses between zota+ omega n CS strains and some zota- CREO mutants: the zota- CREO are unable to integrate by recombination their CR allele into the zota+ mit-DNA of omega n CS strains while being capable of integrating it into omega+ CS or omega- CS genomes . 3 . It is proposed that the omega locus is the site of initiation of non reciprocal recombination events, the omega+/omega- pairing specifically init