Mol Gen Genet, 1981, 182(2), 196 - 205 Repair of interstrand cross-links in DNA of Saccharomyces cerevisiae requires two systems for DNA repair: the RAD3 system and the RAD51 system; Jachymczyk WJ et al.; We have studied the role of the excision-repair system and the recombination-repair system in the removal of cross-links and monoadducts caused by furocoumarins plus 360 nm radiation in yeast DNA by neutral and alkaline sucrose gradients and by a fluorometric procedure which detects cross-linked DNA molecules . We found that the excision-repair system, represented by the rad3 mutations, is required both for the removal of monoadducts, causing single-strand break formation, and for the removal of cross-links, causing double-strand break formation . The recombination-repair system, represented by the rad51 mutation, is necessary for double-strand break repair following cross-link removal, but it has no role in the repair of monoadducts . It can be concluded, that at least some of the same enzymes are used in yeast for both the excision of pyrimidine dimers and the excision of cross-links or monoadducts caused by furocoumarins plus light . The RAD3 and RAD51 repair systems, which act independently in the repair of UV-induced lesions, are part of a single system for the repair of cross-links. Antonie Van Leeuwenhoek, 1981, 47(3), 193 - 207 Extracellular protein release and its response to pH level in Saccharomyces cerevisiae; Weller J et al.; Saccharomyces cerevisiae grown in batch culture at pH 5.5 releases 0.1 to 0.2 pg protein per cell to the external medium over a period of four to five days, final concentration 20-40 micrograms/ml . Cells grown at pH 3.0 release 10-fold this quantity (1-2 pg/cell, final concentration 100-200 micrograms/ml) . A kinetic model based on published behavior of periplasmic protein gave a good fit to the observed kinetics of exoprotein yield . The electrophoretic pattern of exoprotein differed from that of cell lysate protein, and exoprotein synthesis was apparently limited to early stages of the life cycle . These results are consistent with the identification of exoprotein as periplasmic protein released to the external medium through the cell wall . Analysis of the observed kinetics of exoprotein yield, utilizing the kinetic model suggests that the greater exoprotein production of cells grown at pH 3.0 was due entirely to greater synthesis of periplasmic proteins while the fraction of periplasmic protein released per unit time was greater for cells grown at pH 5.5 . The latter conclusion is supported by thicker cell walls of cells grown at pH 3.0 as observed by electron microscopy . At an applied level the apparent limitation of exoprotein synthesis to the first few hours of cell life, the slow leakage of exoprotein through the cell wall, and the dilute nature of a yeast suspension do not favor the utilization of yeast cells for direct conversion of substrate into protein released to the external medium. Mol Gen Genet, 1981, 182(1), 1 - 6 Sporulation of products of protoplast fusion without regeneration in Saccharomyces cerevisiae; Tsuboi M; In Saccharomyces cerevisiae, diploid strains which are respiratory deficient (e.g., rho-) or are homozygous for the mating-type locus (i.e., either a/a or alpha/alpha) are unable to sporulate . In order to induce sporulation in these nonsporulating strains, the technique of protoplast fusion mediated by polyethylene glycol was adopted . In this study, the products of protoplast fusion were induced to sporulate without reversion to normal cells . Protoplasts from a respiratory-deficient diploid strain were mixed with those from a respiratory-competent haploid one carrying mitochondrial drug resistance markers, treated with 30% polyethylene glycol-4000 and 25 mM CaCl2, and incubated in 0.1 M potassium acetate containing 0.8 M sorbitol as an osmotic stabilizer . After two days' incubation, asci with three to eight spores were formed at a frequency of 1 x 10(-3) to 2 x 10(-4) . Sporulation was also observed in products of fusion between an a/a diploid and alpha haploid strains and between an alpha/alpha diploid and a haploid strains . The analysis of the genotypes of spores revealed that when fusion products were cultured under conditions for sporulation, karyogamy did not take place, diploid nuclei underwent meiosis, and both diploid and haploid nuclei were able to develop into spores. Genetics, 1981 Jan, 97(1), 45 - 64 Protein degradation, meiosis and sporulation in proteinase-deficient mutants of Saccharomyces cerevisiae; Zubenko GS et al.; During the process of sporulation, a/alpha diploids degrade about 50% of their vegetative proteins . This degradation is not sporulation specific, for asporogenous diploids of a/a mating type degrade their vegetative proteins in a fashion similar to that of their a/alpha counterparts . Diploids lacking carboxypeptidase Y activity, prc1/prc1, show about 80% of wild-type levels of protein degradation, but are unimpaired in the production of normal asci . Diploids lacking proteinase B activity, prb1/prb1, show about 50% of wild-type levels of protein degradation . The effect on degradation of the proteinase B deficiency is epistatic to the degradation deficit attributable to the carboxypeptidase Y deficiency . The prb1 homozygotes undergo meiosis and produce spores, but the asci and, possibly, the spores are abnormal . Diploids homozygous for the pleiotropic pep4-3 mutation show only 30% of the wild-type levels of degradation when exposed to a sporulation regimen, and do not undergo meiosis or sporulation . Neither proteinase B nor carboxypeptidase Y is necessary for germination of spores . Approximately half of the colonies arising from a/a or alpha/alpha diploids exposed to the sporulation regimen that express an initially heterozygous drug-resistance marker (can1) appear to arise from mating-type switches followed by meiosis and sporulation. Antonie Van Leeuwenhoek, 1981, 47(2), 121 - 31 induction and derepression of arginase and ornithine transaminase in different strains of Saccharomyces cerevisiae; Middelhoven WJ et al.; The syntheses of arginase and ornithine transaminase were studied in two strains of Saccharomyces cerevisiae, viz . strain B and strain alpha-sigma 1278b . Derepression of both enzymes during nitrogen starvation was shown only by strain B, non-specific induction of arginase only by strain alpha-sigma 1278b . This different response of both strains studied reveals substantial differences in the regulation of enzyme synthesis among yeast strains of one and the same species . The specific enzyme activities observed in chemostat cultures with arginine as the nitrogen source and different sugars, at variable carbon to nitrogen ratios, did not indicate the involvement of carbon catabolite repression in the regulation of arginase and ornithine transaminase syntheses . Specific arginase activities observed in the continuous cultures varied widely and did not show a correlation with the intracellular arginine concentration . Extracellular steady-state arginine concentrations higher than about 1.0 mM, in addition to abundant energy supply, were found to be required for high production of arginase . It is suggested that, besides intracellular arginine, extracellular arginine may provide an induction signal necessary for full-scale induction of arginase synthesis . A possible intermediary role of arginine permeases or of other membrane proteins is discussed. Genetika, 1981, 17(6), 1000 - 8 {Genetic effects of the breakdown of tritium incorporated into Saccharomyces cerevisiae yeast cells . IV . The lethal and mutagenic effects and the nature of the mutations induced by tritium breakdown in the 5th position of cytosine}; Ivanov EL et al.; We have studied in lethal and mutagenic effects and the nature of mutations induced by 3H decays in the 5-th position of cytosine (5-3H-C) . The lethal efficiency was determined as alpha 1 = (10.3 +/- 6.7) x 10(-3) decay-1 or alpha 1 = (12.9 +/- 9.4) x 10(-5) rad-1 and the mutagen efficiency for ade1, ade2 genes -- as alpha m = (4.3 +/- 2.3) x 10(-7) decay-1 or alpha m = (5.4 +/- 2.9) x 10(-9) rad-1 . For ade2 gene the spectrum of mutations induced by 5-3H-C was as follows: 1% of frameshifts and 99% of base pair substitutions -- 9% of transversions, 3% of AT leads to GC transitions and 87% of GC leads to AT transitions . Our results establish the 5-3H-C as one of the most effective and specific mutagens reported so far for yeast . According to the scheme of Krasin with coworkers, the final product of 3H decay in the 5-th position of cytosine is uracil . Our calculations show that more than 90% of uracil residues are removed from the yeast genome by cell repair systems. Genetika, 1981, 17(5), 822 - 31 {Mechanism of mutant induction in the ade2 gene of diploid Saccharomyces cerevisiae yeasts by ultraviolet rays}; Gordenin DA et al.; Ultraviolet light (UV) at 3000 ergs/mm-2 induces ade2 mutants with a frequency about 10(-4) in wild-type haploid strains of yeast and about 10(-5) in diploid wild-type strains . UV irradiation effectively induced mitotic segregation of ade2 in the heterozygous diploid (the frequency of segregation is 6%) . Interallelic complementation and localization spectra are similar for mutations induced both in haploids and diploids . The occurrence of ade2 mutants in diploids correlated with mitotic segregation of the marker his8 which is situated in the same arm of XY chromosome as ade2 is, distal to the centromere . Our data about the frequency of ade2 mutants in diploids and haploids, the frequency of ade2 mitotic segregation, mitotic segregation of other markers and genetic characteristics of ade2 mutations confirm the suggestion that the major mechanism of diploid ade2 mutants appearance is mutation in one of the two ADE2 alleles and consequent mitotic homozygotisation of mutation as a result of mitotic crossingover between ade2 and the centromere. Genetika, 1981, 17(3), 405 - 10 {Genetic effects of N-nitroso-N-methylurea on Saccharomyces cerevisiae . II . Effect of radiosensitivity mutations on lethal and mutagenic effects}; Iadgarov KhT; Study of the lethal effect of NMU on radiosensitive strains rad2, rad54 and xrs2 of Saccharomyces cerevisiae has demonstrated that the mutations rad2 and rad54 increase the sensitivity of these strains to low doses of the mutagen . Mutations rad2, rad54 and xrs2 decreases the mutagenic effect of NMU . The study of nature of mutations induced by NMU in ade2 locus has shown that they are mainly the base substitutions . Mutations of radiosensitivity do not influence the nature of NMU-induced mutations in ade2 locus. Proc Natl Acad Sci U S A, 1981 Jan, 78(1), 435 - 9 Mutant defective in processing of an enzyme located in the lysosome-like vacuole of Saccharomyces cerevisiae; Hemmings BA et al.; Carboxypeptidase Y, a vacuolar enzyme in Saccharomyces cerevisiae, is synthesized as a larger precursor whose apparent molecular mass is approximately 67,000 daltons . We have characterized a recessive mutation, pep4-3, that prevents maturation of this precursor . The accumulated precursor does not possess enzymatic activity . We have shown that the precursor accumulating in the pep4-3 mutant is not produced in a doubly mutant strain that also bears a mutation in the carboxypeptidase Y structural gene that eliminates production of carboxypeptidase Y . We have also shown that a nonsense fragment of carboxypeptidase Y is processed . Although there is evidence that proteinase B can catalyze the conversion of the precursor to a mature form in vitro, nonsense mutations in the structural gene for proteinase B, PRB1, do not affect the levels of carboxypeptidase Y activity, and strains bearing these mutations produce a carboxypeptidase Y of apparently normal size . Hence, proteinase B is not essential for the maturation of carboxypeptidase Y precursor in vivo . The pep4-3 mutation affects at least five vacuolar enzymes . This suggests that there is a processing event common to all of these enzymes. Can J Genet Cytol, 1981, 23(1), 73 - 9 Pure and mosaic clones--a reflection of differences in mechanisms of mutagenesis by different agents in Saccharomyces cerevisiae; Nasim A et al.; The induction of pure and mosaic clones has been studied in haploid G1 cells of Saccharomyces cerevisiae . Following treatments with ultraviolet light, methyl methanesulfonate, ethyl methanesulfonate, nitrous acid, and N-methyl-N'-nitro-N-nitrosoguanidine, the relative proportions of pure mutant clones varied from 25 to 100% at comparable survival levels . Ultraviolet light and methyl methanesulfonate produced mainly pure mutant clones, whereas ethyl methanesulfonate and nitrous acid produced mainly mosaics at 59 to 100% survival levels . The ratio of pure to mosaic clones induced by nitrosoguanidine fell between these two classes . These results are consistent with a classification of mutagens on the basis of repair and replication-dependent mechanisms of mutagenesis in other organisms . Agents having actions similar to ultraviolet light may produce mainly pure clones through a pre-replicative process involving an error-prone DNA repair process . Others may produce mainly mosaic mutants due to the different nature of DNA lesions which may require a replication-dependent process for fixation of mutations . Preliminary data from combined treatments of mutagens belonging to two different classes (i.e . ultraviolet light and nitrous acid) suggest the possibility of an interaction between these agents, resulting in a higher proportion of pure clones, possibly due to an inducible process . Studies of induced frequencies of pure and mosaic clones may be useful in the characterization of mutagens with functional differences. Z Allg Mikrobiol, 1981, 21(1), 53 - 5 Effects of chloramphenicol on the thermal profile of Saccharomyces cerevisiae; Madeira-Lopes A et al.; Chloramphenicol decreased the maximum temperature for growth of a petite mutant of Saccharomyces cerevisiae, shifted the ARRHENIUS plot of thermal death to lower temperatures and shortened correspondingly, the ARRHENIUS plot of growth, while an associative thermal profile was maintained . At saturating concentrations (about 5 mg per ml) of chloramphenicol in liquid mineral medium with vitamins and glucose the final maximum temperature for growth was depressed from about 40 degrees C to about 37 degrees C . The results suggested that chloramphenicol acted in the mutant on targets other than mitochondrial ribosomes and that these targets are identical or associated with the death and Tmax sites of the yeast. Mutat Res, 1981 Jan, 80(1), 91 - 7 Induction of petite "mutants" in an ethidium-resistant strain of Saccharomyces cerevisiae by photoaffinity labeling . Distinction between early and late steps; Fukunaga M et al.; A strain of Saccharomyces cerevisiae (MH41-7B/011) was resistant to petite induction by ethidium bromide at 30 degrees, but was sensitive to induction by photolabeling with ethidium monoazide . These results suggested a defect in the mutant in metabolic activation of ethidium to account for its resistance . Synchronized cultures of both the mutant and the normal parent strains showed a substantial reduction in petite response to photolabeling in stationary phase cells which could not be accounted for by changes in cell penetration of the drug . The use of photolabeling with normal and mutant cells suggested that petite induction can be divided into early and late steps. Eur J Biochem, 1981 Jan, 113(2), 327 - 31 Synthesis of Saccharomyces cerevisiae catalase A in vitro; Ammerer G et al.; mRNA isolated from cells of the yeast Saccharomyces cerevisiae was translated in the cell-free protein synthesis system from wheat germ . Catalase proteins synthesized were isolated from incubation mixtures by immunoadsorption followed by polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulfate . On dodecyl sulfate gels catalase A synthesized by the wheat germ system migrates like catalase A protein synthesized in vivo . Evidence is presented that yeast catalase T and A synthesized in vivo are no glycoproteins . Synthesis of the two catalase proteins in the wheat germ system and dissimilarity of proteolytic fingerprints of the two proteins demonstrate conclusively that catalase T and A are biogenetically unrelated. J Bacteriol, 1981 Jan, 145(1), 221 - 32 Structure and function of the PHO82-pho4 locus controlling the synthesis of repressible acid phosphatase of Saccharomyces cerevisiae; Toh-e A et al.; pho4 mutants of Saccharomyces cerevisiae, although rare among phosphatase-negative mutants isolated from wild-type strains, were isolated efficiently from pho80, pho85, or pho80 pho85 strains . The distribution of these pho4 mutants over the pho4 locus was determined by analyzing random spores of two- and three-factor crosses . The pho4-4 mutation confers temperature-sensitive synthesis of repressible acid phosphatase . An intragenic suppressor for the pho4-12 allele results in the temperature-sensitive synthesis of repressible acid phosphatase . Recombination between these sites occurs at 1.0 to 3.0%, the highest for any pair of sites within the pho4 locus . All these results strongly indicate that the information of the pho4 locus is translated into a protein . The PHO82 site was mapped inside the pho4 locus by random spore analysis . The order met10-pho4-1PHO82-1-pho4-9 on the right arm of chromosome VI was confirmed by tetrad analysis . Doubly heterozygous diploids, pho3 PHO82c PHO4+/pho3 pho82+ pho4, produce variable amounts of repressible acid phosphatase under repressive conditions depending on the combination of PHO82c and pho4 alleles . This phenomenon may reflect the constitutive production of the pho82+-pho4 product in the repressed condition, which interferes with the function of the PHO82c-PHO4+ product . The earlier model for the function of the PHO82-pho4 cluster, in which the PHO82 site acts as an operator of the pho4 gene, has been revised to a model in which the PHO82 site codes for the part of the pho4 protein that has affinity for the regulatory protein encoded by the pho80 and pho85 genes. Mol Cell Biol, 1981 Jan, 1(1), 9 - 12 Temperature-sensitive glucosamine auxotroph of Saccharomyces cerevisiae; Ballou L et al.; Temperature-sensitive revertants were isolated from Saccharomyces cerevisiae D-glucosamine auxotrophs previously obtained in this laboratory (W . L . Whelan and C . E . Ballou, J . Bacteriol . 124:1545-1557, 1975) . The auxotrophs lack the enzyme 2-amino-2-deoxy-D-glucose-6-phosphate ketol-isomerase (EC 5.3.1.19), and the revertants appear to be temperature sensitive in the formation of enzyme activity . The enzyme they produce under permissive conditions decays in activity at a rate comparable to that of the wild-type enzyme, and it has similar kinetic properties . The homozygous diploid mutant fails to sporulate at the nonpermissive temperature . Temperature shift experiments were carried out in an effort to determine what effect glucosamine deficiency had on mannoprotein secretion as reflected in the formation of external asparaginase . Although the results were complicated by the slow decay of the residual ketol-isomerase activity, they did show that mannoprotein synthesis or secretion was altered when the internal pool of D-glucosamine was depleted. Mol Cell Biol, 1981 Jan, 1(1), 51 - 7 Characterization of a 40S ribosomal subunit complex in polyribosomes of Saccharomyces cerevisiae treated with cycloheximide; Helser TL et al.; Under specific conditions cycloheximide treatment of Saccharomyces cerevisiae caused the accumulation of a type of polyribosome called "halfmer." Limited ribonuclease digestion of halfmers released particles from the polyribosomes identified as 40S ribosomal subunits . The data demonstrated that halfmers are polyribosomes containing an additional 40S ribosomal subunit attached to the messenger ribonucleic acid . Protein gel electrophoretic analysis of halfmers revealed numerous nonribosomal proteins . Two of these proteins comigrate with subunits of yeast initiation factor eIF2. Cancer Detect Prev, 1981, 4(1-4), 53 - 7 Recombinogenic activity of fresh cigarette smoke in Saccharomyces cerevisiae; Gairola CC et al.; A procedure for determining the effect of fresh cigarette smoke on gene conversion in yeast . Saccharomyces cerevisiae D7, is described . Cigarette smoke, generated by a 2-sec, 40-ml puff, once per minute, was puffed into an open-end tube . The smoke was drawn through an exposure vessel containing a continuously stirred, stationary-phase yeast cell suspension, 1-58 sec after generation . Frequency of gene conversion was estimated in samples taken at intervals after the start of exposure . Under these conditions, a five-fold increase in mitotic gene conversion in yeast strain D7 was obtained from exposure to 20 puffs of fresh whole smoke from University of Kentucky Reference Cigarettes (2R1), to 75 puffs from the gas phase of these cigarettes, and to 45 puffs from an acetate filter version (2R1F) . Selective removal of genetically active components by acetate filters is suggested since the reduction in recombinogenic activity (55%) is greater than the reduction in total particulate matter yield (25%) of the cigarette . The results indicate that 1) the procedure provides a practical bioassay for determining the effects of fresh smoke on gene conversion in yeast, without external metabolic activation; 2) the gas phase of smoke has recombinogenic activity; and 3) standard acetate filters may selectively remove genetically active components of cigarette smoke. C R Seances Soc Biol Fil, 1981, 175(6), 835 - 9 {Possible transfer between sarcomatous mouse cells (BP8) and yeasts (Saccharomyces cerevisiae, whole bodies and protoplasts)}; Miegeville M et al.; From our observation in vitro, we can suggest that : a direct contact between sarcomatous cells and physiologically active yeasts appears to be necessary for the transfer of the radioactive labelling; the presence of a filter with pores of 1.2 micrometer diameter prevents passage of fragments of DNA or RNA between the cells; this transfer is a very small fact, but implies about the third of the yeasts. J Mol Appl Genet, 1981, 1(3), 239 - 44 The nucleotide sequences of the actin genes from Saccharomyces carlsbergensis and Saccharomyces cerevisiae are identical except for their introns; Nellen W et al.; The actin gene from yeast Saccharomyces carlsbergensis was cloned in Escherichia coli and its complete nucleotide structure was determined . A comparison of its DNA sequence with that of the related yeast species Saccharomyces cerevisiae revealed that the coding as well as the 5'- and 3'-untranslated regions are identical . The intron, although at the same location in the two genes, differs in three positions . There is one deletion (or insertion), one transition, and one transversion . These are clustered within and around an oligo(dA) stretch of 14 (or 13) residues . Our observations identify the intron as the fastest evolving segment of this eukaryotic gene. Mol Gen Genet, 1981, 182(3), 456 - 61 Construction of hybrid plasmids containing the lysA gene of Escherichia coli: studies of expression in Escherichia coli and Saccharomyces cerevisiae; Chenais J et al.; The lysA gene of Escherichia coli has been cloned from a lambda transducing phage on various plasmids, present in different copy numbers in bacterial cells . Synthesis of the product of this gene, diaminopimelate (DAP)-decarboxylase, and its regulation have been studied . Expression does not follow a simple gene dosage effect, maximal expression already being obtained with a six-copy plasmid . This result suggests that either a positive or an autogenous regulatory mechanism is involved . We also used one of the hybrid plasmids to look for expression of the bacterial lysA gene in Saccharomyces cerevisiae . The results indicate that the product of the E . coli gene is not actively translated in yeast. Mol Gen Genet, 1981, 182(1), 159 - 63 Analysis of mutations affecting Ty-mediated gene expression in Saccharomyces cerevisiae; Ciriacy M et al.; Yeast translocatable, Ty, elements can cause constitutive synthesis of the glucose-repressible alcohol dehydrogenase (ADHII) when inserted upstream from the 5' end of the structural gene, ADR2 . These insertion mutations, ADR3c, are unstable and give rise to secondary ADHII- mutations . The majority of such mutants, adr3, can be attributed to excision of the insertion sequence, leaving behind a single copy of the delta-sequence which occurs as a direct repeat at the ends of the Ty elements . A few adr3 mutants appear to be generated by DNA-rearrangements in the vicinity of the Ty insertion . The occurrence of recessive mutants, tye, which are unlinked to ADR2 indicates that the constitutive expression of ADR2 caused by the Ty insertions requires the function of trans-acting genes . These results support the idea that regulation of Ty-linked ADR2 is actively mediated by the insertion sequence and is probably not due to a mere disruption of the wild-type controlling site. Acta Microbiol Pol, 1981, 30(2), 111 - 21 Isolation and properties of elongation factor 1 from Saccharomyces cerevisiae; Palen E et al.; Polypeptide elongation factor 1 was isolated from yeast postribosomal supernatant . The highly purified factor was resolved on Ultrogel AcA-44 into two complementary fractions . One of these fractions contained two different polypeptide chains corresponding to a Ts-like elongation factor EF-1 beta gamma . The other fraction represented the light form of the factor, designated EF-1 alpha, with a molecular weight of approximately 50,000 . The obtained results indicate that EF-1 from lower eukaryotes is also composed of three distinct polypeptides. J Biol Chem, 1980 Dec 25, 255(24), 11892 - 5 Effect of glucosylation of lipid intermediates on oligosaccharide transfer in solubilized microsomes from Saccharomyces cerevisiae; Trimble RB et al.; Glc3Man9GlcNAc2-P-P-dolichol and Man9GlcNAc2-P-P-dolichol isolated from Saccharomyces cerevisiae are substrates for the N-glycosylation of endogenous proteins in Triton X-100-solubilized yeast microsomes . The solubilized oligosaccharide transferase requires Mn2+ for activity; neither Mg2+ nor Ca2+ is an effective substitute . The pH optimum of the transfer reaction is between 6.5 and 7.5 . Unlike animal systems, which utilize glucosylated oligosaccharide-lipid to a much greater extent than the unglucosylated species as a donor in the transferase rection, yeast extracts transfer more than 70% of Glc3Man9GlcNAc2 and Man9GlcNAc2 from their respective oligosaccharide-lipids to proteins . However, the rate of N-glycosylation in vitro is approximately 25-fold faster with Glc3Man9GlcNAc2-P-P-dolichol than with Man9GlcNAc2-P-P-dolichol . The apparent Km value for the glucosylated species is 75 nM, while that for the unglucosylated glycolipid is 55 nM. J Biol Chem, 1980 Dec 25, 255(24), 11704 - 9 RNA-dependent ATPase from Saccharomyces cerevisiae; Belhadj O et al.; A new RNA-dependent ATPase has been isolated from yeast chromatin extracts and partially characterized . The protein has a sedimentation coefficient of about 7 S . The enzyme hydrolyzes specifically ATP (or dATP) to ADP (or dADP) and Pi in the presence of Mg2+ or Mn2+ ions and requires a single-stranded polynucleotide as cofactor . The order of efficiency of synthetic polymers is poly(rU) > poly(rI) greater than or equal to poly(dU) > poly(rA) greater than or equal to poly(rC) . Among natural polymers, single-stranded DNA and poly(rA)-containing mRNA from yeast are also active but less so than poly(rU) . The enzyme exhibits a pH optimum of 8 and is fully inhibited by 0.25 M NaCl . The Km for ATP is0.2 mM . The resemblance between this ATPase and DNA-dependent ATPases from other sources, as well as the termination factor rho, is discussed. Nucleic Acids Res, 1980 Dec 11, 8(23), 5779 - 94 The structure of the yeast ribosomal RNA genes . I . The complete nucleotide sequence of the 18S ribosomal RNA gene from Saccharomyces cerevisiae; Rubtsov PM et al.; The cloned 18 S ribosomal RNA gene from Saccharomyces cerevisiae have been sequenced, using the Maxam-Gilbert procedure . From this data the complete sequence of 1789 nucleotides of the 18 S RNA was deduced . Extensive homology with many eucaryotic as well as E . coli ribosomal small subunit rRNA (S-rRNA) has been observed in the 3'-end region of the rRNA molecule . Comparison of the yeast 18 S rRNA sequences with partial sequence data, available for rRNAs of the other eucaryotes provides strong evidence that a substantial portion of the 18 S RNA sequence has been conserved in evolution. Biochim Biophys Acta, 1980 Dec 4, 616(2), 271 - 82 Asparaginase II of Saccharomyces cerevisiae: inactivation during the transition to stationary phase; Pauling KD et al.; Asparaginase II (L-asparagine amidohydrolase, EC 3.5.1.1) activity of cells from stationary phase cultures of Saccharomyces cerevisiae is very low . When these cells are inoculated into minimal medium, asparaginase II specific activity rises rapidly and reaches a maximum after 9-10 h . During the next 2.5-3 h, a rapid decrease in asparaginase II specific activity occurs . The enzyme does not appear to be secreted into the medium or to be reabsorbed into the cell . Addition of protease inhibitors at the time of maximum activity partially or totally prevents the loss of asparaginase II . L-1-Tosylamide-2-phenylethyl chloromethyl ketone decreases the rate of loss . The sulfhydryl reagents p-hydroxymercuribenzoate and iodoacetamide inhibit the loss of asparaginase II . However, addition of EDTA causes a further increase in activity . This increase is due to de novo protein synthesis . The effect of EDTA can be reversed by the addition of Zn2+ . The most likely explanation for the rapid loss of asparaginase II is proteolytic degradation by a Zn2+-dependent, thiol protease or peptidase. Genetics, 1980 Dec, 96(4), 859 - 76 Diploid spore formation and other meiotic effects of two cell-division-cycle mutations of Saccharomyces cerevisiae; Schild D et al.; The meiotic effects of two cell-division-cycle mutations of Saccharomyces cerevisiae (cdc5 and cdc14) have been examined . These mutations were isolated by L.H . HARTWELL and his colleagues and characterized as defective in mitosis, causing a temperature-sensitive arrest in late nuclear division . When subjected to the restrictive temperature in meiosis, diploid cells homozygous for either of these mutations generally proceeded through premeiotic DNA synthesis and commitment to meiotic levels of recombination, but then arrested at a stage following spindle pole body (SPB) duplication and separation . The two SPBs lacked the interconnection by spindle microtubules typical of the complete meiosis I spindle . Challenge of these homozygotes by a semi-restrictive temperature often caused the production of asci containing two diploid spores . Genetic analysis of the viable pairs of spores revealed that each spore had become homozygous for centromere-linked markers significantly more frequently than for distal markers, indicating that the two spores each contained pairs of sister centromeres that had co-segregated in the reductional division of meiosis I . Ultrastructural analysis of the cdc5 homozygote demonstrated that these cells had completed meiosis I and formed two meiosis II spindles, but that the latter remained unusually short . This resulted in the encapsulation of both poles of each spindle within a single spore wall . These mutations therefore are defective in both meiotic divisions, as well as in the mitotic division described originally. Genetics, 1980 Dec, 96(4), 819 - 39 The origin of spontaneous mutation in Saccharomyces cerevisiae; Quah SK et al.; Characterization of two antimutator loci in yeast shows that both are members of the same mutagenic repair system known to be responsible for almost all induced mutation (LAWRENCE and CHRISTENSEN 1976, 1979a,b; PRAKASH 1976) . One of the these newly isolated antimutator mutations is an allele of rev3 (LEMONTT 1971b) . Two other alleles of rev3 were tested and were also found to be antimutators . Double mutants carrying rev3 and mutator mutations of rad3, rad51 or rad18 are like rev3 single mutants with respect to spontaneous mutation rate, supporting the hypothesis (HASTINGS, QUAH and VON BORSTEL, 1976) that many mutators in yeast act by channelling spontaneous lesions from accurate to mutagenic repair . However, the enhanced mutation rate seen in a radiation-resistant mutator mutant mut1 is not dependent on REV3, but is dependent on another gene designated ANT1 . An additive effect on the reduction in spontaneous mutation, seen in the ant1 rev3 double-mutant strain, leads to the conclusion that at least 90% of spontaneous mutations seen in the wild type are caused by mutagenic repair of spontaneous lesions. Antimicrob Agents Chemother, 1980 Dec, 18(6), 863 - 7 Binding of cycloheximide to ribosomes from wild-type and mutant strains of Saccharomyces cerevisiae; Stocklein W et al.; Cycloheximide bound to cytoplasmic (80S) ribosomes of the yeast Saccharomyces cerevisiae with an association constant (Ka) of 2.0 (+/- 0.5) x 10(7) M-1 . The number of binding sites found per ribosome was between 0.4 and 0.6; it was reduced by high-salt treatment of ribosomes 60S particles prepared in the presence of high salt had a lower affinity (Ka: 5.5 {+/- 0.5} x 10(6) M-1) than did 80S ribosomes, but a greater proportion of particles (0.8) were able to bind . No specific binding to 40S subunits was observed . The addition of supernatant fractions (S100, high-salt wash fraction) increased the number of binding sites found per 80S ribosome up to 0.8, leaving the association constant unchanged . In contrast, the affinity of 60S subunits was enhanced to a Ka value of 3.5 x 10(-7) M-1 by the addition of supernatant fractions, whereas the number of binding sites stayed constant . A model to explain these facts is proposed . 80S ribosomes, as well as 60S subunits of strain cy32, which is highly resistant to cycloheximide and altered in ribosomal protein L29 (18), showed a drastically reduced affinity for the drug (Ka values of 2.0 x 10(6) M-1). J Cell Sci, 1980 Dec, 46, 341 - 52 The influence of the microtubule inhibitor, methyl benzimidazol-2-yl-carbamate (MBC) on nuclear division and the cell cycle in Saccharomyces cerevisiae; Quinlan RA et al.; Methyl benzimidazol-2-yl-carbamate (MBC), at a concentration of 100 microM, has a pronounced effect on the growth of Saccharomyces cerevisiae, resulting in the accumulation of cells as large doublets . We have determined a specific execution point for the effect of MBC on the yeast cell cycle, and have shown that this execution point is between the cycle events of spindle pole body duplication and spindle pole body separation . An ultrastructural examination of the MBC-treated cells revealed the absence of cytoplasmic and spindle microtubules . MBC treatment also produced an altered spindle pole body morphology, causing the disappearance of the outer component . Nuclear size was also markedly increased in the MBC-induced doublet cells, although the septa were completely absent from these doublet cells . It is proposed that MBC inhibits microtubule polymerization, rather than causing the depolymerization of stable microtubules. Gene, 1980 Dec, 12(1-2), 1 - 10 Expression of the HIS3 gene of Saccharomyces cerevisiae in polynucleotide phosphorylase-deficient strains of Escherichia coli K-12; Kasunic DA et al.; The PstI and BamHI fragments, containing the HIS3 (imidazoleglycerol phosphate dehydratase) gene of yeast obtained from pYehis2, and the ColE1-derived plasmid pBR322 were ligated in vitro and used to transform hisB463 strains of Escherichia coli K-12 . Expression of the cloned HIS3 gene from yeast was markedly enhanced (3--5-fold) in polynucleotide phosphorylase (pnp)-deficient strains of E . coli . The levels of both HIS3 and plasmid-encoded mRNAs were increased in pnp- strains carrying the chimeric plasmids, whereas there was little difference in the levels of pBR322-specific mRNAs in pnp+ and pnp- strains . This increase in HIS3 mRNA appeared to be related to specific stabilization of the eukaryotic message due to its unique structural features, since the half-life of the HIS3 mRNA increased from 1.5 to 18.7 min, whereas no increase in the half-lives of pBR322 vehicle mRNAs was observed . A physical map of the plasmid pYehis2 was constructed using restriction endonuclease and molecular cloning techniques. J Bacteriol, 1980 Dec, 144(3), 1143 - 51 Identification of an actin-like protein and of its messenger ribonucleic acid in Saccharomyces cerevisiae; Water RD et al.; We have identified a yeast protein that resembles actins from other eucaryotes in its tight binding to pancreatic deoxyribonuclease I, its copolymerizaton with purified muscle actin, its one-dimensional peptide map, and its apparent polymerization into 7-nm filaments . The yeast actin-like protein yielded a single spot on two-dimensional polyacrylamide gel electrophoresis, suggesting that a single protein species was present . On sodium dodecyl sulfate-polyacrylamide gel electrophoresis, the actin-like protein had an apparent molecular weight of 45,000 compared with 42,000 for muscle actin . In an attempt to identify the messenger ribonucleic acid coding for the actin-like protein, yeast polyadenylic acid-rich ribonucleic acid was translated in wheat germ and reticulocyte cell-free protein-synthesizing systems . The actin-like protein was identified among the translation products of the reticulocyte system by its tight binding to deoxyribonuclease I, its comigration with the in vivo-synthesized actin-like protein during sodium dodecyl sulfate-polyacrylamide gel electrophoresis, an the similarity of its peptide map to that of the in vivo-synthesized protein . A yeast protein synthesized in the wheat-germ system was also found to bind to deoxyribonuclease I and to copolymerize with muscle actin . However, its apparent molecular weight was about 35,000, suggesting that it was a product either of incomplete translation or of proteolytic cleavage of the actin-like protein. J Bacteriol, 1980 Dec, 144(3), 1113 - 8 Isolation and characterization of temperature-sensitive mak mutants of Saccharomyces cerevisiae; Guerry-Kopecko P et al.; The K1 killer plasmid of Saccharomyces cerevisiae is a 1.5-megadalton linear double-stranded ribonucleic acid molecule . Using simplified screening and complementation procedures, we have isolated mutants in three chromosomal genes that are temperature sensitive for killer plasmid maintenance or replication . One of these genes, mak28-1, was located on chromosome X . Two of the temperature-sensitive mutants rapidly lost the wild-type killer plasmid of A364A during spore germination and outgrowth at nonpermissive temperatures, but during vegetative growth, they only lowered the plasmid copy number . These two mutants did not lose two other wild-type K1 killer plasmids, indicating a heterogeneity of the killer plasmids in laboratory yeast strains. Gene, 1980 Dec, 12(1-2), 41 - 9 3 micron DNA - an extrachromosomal ribosomal DNA in the yeast Saccharomyces cerevisiae; Larionov VL et al.; A new class of extrachromosomal DNA which consists predominantly of covalently closed molecules with lengths around 3 micron, has been detected in Saccharomyces cerevisiae strain 6-1G-P188 from the Peterhof collection . Restriction analysis of the 3 micron DNA as well as of recombinant plasmids carrying HindIII fragments of the 3 micron DNA permitted construction of a physical map of the new extrachromosomal DNA species, and detection of two types differing by one EcoRI restriction site . Molecular hybridization, as well as comparison of the restriction maps, revealed the complete structural identity of the 3 micron DNA with a chromosomal repetitive unit of rDNA containing the genes for 25 S, 18 S, 5.8 S and 5 S rRNAs. Biochem J, 1980 Nov 15, 192(2), 659 - 64 Membrane proteins associated with amino acid transport by yeast (Saccharomyces cerevisiae); Woodward JR et al.; Cells of the wild-type yeast (Saccharomyces cerevisiae) strain Y185, grown under conditions that de-repress the formation of a general amino acid permease ('Gap') system, bind delta-N-chloroacetyl{1-(14)C}ornithine; L- and D-amino acid substrates of the general amino acid permease system protect against this binding . The protein responsible is released from the cells by homogenization or by preparation of protoplasts; it is not released by osmotic shock . This protein is virtually absent from the wild-type strain when it is grown under conditions that repress the general amino acid permease system, and is also absent from a Gap- mutant Y185-His3, selected by its resistance to D-amino acids . This mutant and repressed wild-type cells also fail to form a number of membrane proteins elaborated by de-repressed wild-type cells . It is possible that all these proteins are components of the general amino acid permease system. Biochemistry, 1980 Nov 11, 19(23), 5456 - 62 Melting of Saccharomyces cerevisiae 5S ribonucleic acid: ultraviolet absorption, circular dichroism, and 360-MHz proton nuclear magnetic resonance spectroscopy; Luoma GA et al.; The heat-induced melting of yeast 5S RNA and tRNAPhe has been monitored by UV, CD, and 360-MHz 1H NMR spectroscopy in order to determine the extent of base stacking and base pairing in the native and denatured structures . In the presence of Mg2+, the optical data indicate less than or equal to 40 base pairs in native yeast 5S RNA, a 60:40 ratio of GC to AU base pairs, with more single-stranded stacking and a slightly less stable structure (half-melted at 67 degrees C) than for tRNAPhe (half-melted at 71 degrees C) . In the absence of Mg2+, the NMR results identify a minimum of approximately 32 base pairs at 25 degrees C (increasing to a minimum of approximately 35 base pairs in the presence of Mg2+), of which more than half are still intact at 48 degrees C . The native structure (25 degrees C) shows only minor dependence upon Mg2+ concentration, and no denatured forms could be detected . Finally, the present results support a previously proposed cloverleaf secondary structure for eukaryotic 5S RNA. J Biol Chem, 1980 Nov 10, 255(21), 10232 - 8 Characterization of large oligosaccharide-lipids synthesized in vitro by microsomes from Saccharomyces cerevisiae; Trimble RB et al.; Conditions are described for optimizing the synthesis of large oligosaccharide-lipids in microsomal preparations from Saccharomyces cerevisiae . On incubating microsomes, with GDP-{14C}Man, the major product obtained was Man9GlcNAc2-P-P-dolichol, but when both GDP-{14C}Man and UDP-{3H}Glc were present in the incubation mixture about half of the Man9GlcNAc2 was elongated to Glc3Man9GlcNAc2-P-P-dolichol . Unlike particulate fractions from mammalian systems, little glucosylation of the yeast microsomal oligosaccharide-lipid was obtained when the concentration of UDP-Glc was less than 10 microM, but the synthesis of this product could be maximized by raising the concentration of UDP-Glc to 50 microM . Analysis of the yeast Man9GlcNAc2 species confirmed that 8 of the 9 mannose residues could be released with alpha-mannosidase, while the remaining mannosyl residue was in the core trisaccharide, Manbeta 1 leads to 4GlcNAc beta 1 leads to 4GlcNAc . Treatment of Glc3Man9GlcNAc2 with alpha-mannosidase released 5 of 9 mannose residues and yielded Glc3Man4GlcNAc2 . This product appeared to be identical with that obtained in parallel experiments with double labeled oligosaccharide-lipid synthesized in oviduct microsomes . Streptomyces plicatus endo-beta-N-acetylglucosaminidase H (Endo-H) treatment of yeast microsomal glycoproteins that were labeled with sugar nucleotides established that 15% of the label was associated with N-linked oligosaccharides . The remaining labeled sugars were released with alkali, indicating that they were linked to serine or threonine . Based on the size and distribution of {3H}glucose and {14C}mannose in the Endo-H-released oligosaccharides, it was concluded that Glc3Man9GlcNAc2 was the primary species transferred to proteins in the yeast system. Mutat Res, 1980 Nov, 73(1), 69 - 79 Differential effect of UV irradiation on induction of intragenic and intergenic recombination during commitment to meiosis in Saccharomyces cerevisiae; Machida I et al.; A comparison was made between the induction of intragenic and intergenic recombinations during meiosis in a wild-type diploid of Saccharomyces cerevisiae . Under non-irradiated normal conditions, production of both intragenic and intergenic recombinants greatly increased in the cells with commitment to meiosis . The susceptibility of cells to the induction of both the spontaneous intra- and intergenic recombinations in meiotic cells was similar . However, under condition of UV irradiation, there were striking differences between intra- and intergenic recombinations . Susceptibility to induction of intragenic recombination by UV irradiation was not enhanced at meiosis compared with mitosis, and was not altered through commitment to meiotic processes . In contrast, however, susceptibility to the induction of intergenic recombination by UV irradiation was enhanced markedly during commitment to meiosis compared with mitosis . Genetic analysis suggested that the enhanced susceptibility to recombination during meiosis is specifically concerned with reciprocal-type recombination (crossing-over) but not non-reciprocal-type recombination (gene conversion) . Hence it is concluded that the meiotic process appears to be intimately concerned with the mechanism(s) of induction of recombination, especially reciprocal-type recombination. Mutat Res, 1980 Nov, 73(1), 59 - 68 Induction of spontaneous and UV-induced mutations during commitment to meiosis in Saccharomyces cerevisiae; Machida I et al.; Inductions of reversions of nonsense, missense and frameshift-type mutations were investigated in a diploid cell population of Saccharomyces cerevisiae during commitment to meiosis, by using the medium-transfer technique from sporulation medium to vegetative medium . The yields of spontaneous reverse mutations obtained from the cells that were committed to different stages during meiosis were rather constant irrespective of the alleles tested, although the yields of both intergenic and intragenic recombinations markedly increased . The susceptibilities to UV-induced reverse mutations examined during commitment to meiosis were not changed appreciably . It is concluded that induction of base-change-type mutations in meiosis is not essentially different from that in mitosis. J Biochem (Tokyo), 1980 Nov, 88(5), 1419 - 23 Occurrence of low molecular weight O-acetylserine sulfhydrylase in the yeast Saccharomyces cerevisiae; Yamagata S; Studies with crude preparations obtained from a cysteine auxotroph of Saccharomyces cerevisiae showed that O-acetylserine sulfhydrylase could be separated from O-acetylhomoserine sulfhydrylase by chromatography on a DEAE-cellulose column and centrifugation in a sucrose density gradient . On the basis of sedimentation distance, the molecular weights of these enzymes were calculated to be about 99,000 and 182,000, respectively . The former did not react with the amino acid substrate of the latter, and vice versa . The wild-type strain was also demonstrated to possess O-acetylserine sulfhydrylase (molecular weight: about 96,000), in addition to a large amount of O-acetylserine-O-acetylhomoserine sulfhydrylase (Yamagata et al . (1974) J . Biochem . 75, 1221). Proc Natl Acad Sci U S A, 1980 Nov, 77(11), 6329 - 33 Autonomously replicating sequences in Saccharomyces cerevisiae; Chan CS et al.; A method is presented for isolating DNA segments capable of autonomous replication from Saccharomyces cerevisiae chromosomal DNA based on the differential transforming ability of autonomously replicating plasmids and nonreplicating plasmids . DNA plasmids that are capable of self-replication in yeast transform yeast spheroplasts at about 1000-fold higher frequency than nonreplicating plasmids . We have cloned from total yeast DNA a number of DNA segments that permit the pBR322 plasmid carrying the yeast LEU2 gene to replicate autonomously . These plasmid clones are characterized by their ability to transform Leu- spheroplasts to Leu+ at a high frequency and their ability to replicate autonomously . Analysis of the insert DNAs carried in some of these self-replicating plasmids divides them into two categories: those that are unique in the yeast genome and those that are repetitive. J Bacteriol, 1980 Nov, 144(2), 852 - 5 Transposed LEU2 gene of Saccharomyces cerevisiae is regulated normally; Kohlhaw GB et al.; The repression of beta-isopropylmalate dehydrogenase, the LEU2 gene product, by leucine and leucine plus threonine was unaffected by the transposition of LEU2 from its original locus on chromosome III to a new locus within the ribosomal deoxyribonucleic acid gene cluster on chromosome XII . Since the expression of the LEU2 gene is probably controlled at a pretranslational level, we conclude that the recombinant plasmid used for transformation carries regulatory information in addition to LEU2 structural information. J Bacteriol, 1980 Nov, 144(2), 826 - 9 Photorepair of ultraviolet-induced petite mutational damage in Saccharomyces cerevisiae requires the product of the PHR1 gene; Green G et al.; A wild-type (phr+) diploid yeast strain showed photorepair of petite mutational damage, whereas a photoreactivation-deficient (phr1/phr1) diploid strain did not, indicating that the PHR1 gene product was required for mitochondrial photorepair. J Antibiot (Tokyo), 1980 Nov, 33(11), 1369 - 75 Isolation and partial characterization of mutants of Saccharomyces cerevisiae altered in sensitivities to lethal effects of bleomycins; Moore CW; Two of eight mutants (bmr) isolated in Saccharomyces cerevisiae on the basis of their increased resistance to lethal effects of antitumor bleomycins (BM), and about two-thirds of 180 yeast mutants (bms) isolated on the basis of their increased sensitivities to cell-killing by phleomycins (PM) or BM were sensitive to one or more of the agents UV, X-rays or hydrogen peroxide, Thus these mutants are likely to be altered in processes acting directly or indirectly on DNA damage . The remaining six bmr mutants and approximately 60 bms mutants appear as resistant as the parent strain to cell-killing by UV or X-rays, and are likely therefore, to be altered in cell wall or membrane function . A genetic basis for the phenotypes of some of the bmr and bms mutants has been established. J Biol Chem, 1980 Oct 25, 255(20), 9821 - 7 Assembly of the mitochondrial membrane system . Complete restriction map of the cytochrome b region of mitochondrial DNA in Saccharomyces cerevisiae D273-10B; Nobrega FG et al.; The cytoplasmic petite (rho-) mutant DS400/A12 has been obtained from the wild type strain of Saccharomyces cerevisiae D273-10B/A21 . The DS400/A12 clone has a mitochondrial genome with a 7.6-kilobase pair, tandemly repeated segment of DNA . Genetic tests indicate that DS400/A12 contains all the cob1 and cob2 markers of the cytochrome b gene . The gene has been further dissected by mutagenesis of DS400/A12 and selection of secondary rho- clones with simpler genotypes . Restriction analysis of the mtDNAs of the rho- clones was used to construct the complete restriction map of the cytochrome b region and to map the mutations within narrowly defined physical limits . The cytochrome b mutants scatter over a maximal distance of 3.3 kilobase pairs . All the mutations assigned previously to the cob2 locus are found between 71.6 and 73.2 units . The cob1 mutations are located between 74.6 and 76.3 units . The estimated distance between the two loci is at least 1 kilobase pair. Biochim Biophys Acta, 1980 Oct 16, 602(1), 201 - 6 Mitochondrial control of cell surface characteristics in Saccharomyces cerevisiae; Evans IH et al.; Defects in the inner mitochondrial membrane of petite mutants of yeast resulted not only in respiratory deficiency, but also in changes in cell surface characteristics . These were (1) concanavalin A agglutinability, (2) cell movement in a biphasic polymer system, (3) cell adhesion . Genetic analysis indicated that the control exerted by the mitochondria was on nuclear genes or on the products of these genes which were presumably specifying cell surface components . These findings ascribe a new role to mitochondria but also have implications for neoplastic transformation. Eur J Biochem, 1980 Oct, 111(2), 357 - 67 Spontaneous dissociation of a cytochrome core and a biglobular flavoprotein after mild trypsinolysis of the bifunctional Saccharomyces cerevisiae flavocytochrome b2; Gervais M et al.; Saccharomyces cerevisiae flavocytochrome b2 is known as a bifunctional enzyme which behaves as the association of an FMN flavodehydrogenase with its specific acceptor, a b5-like cytochrome . Mild trypsinolysis gives rise to three complementary fragments (n, X, beta'), both prosthetic groups being still bound . After such proteolysis the separation of a biglobular flavoprotein domain (carrying FMN) from a cytochrome domain (with the heme) is obtained by molecular sieving under non-denaturing conditions . The marked lack of affinity between the tetrameric flavoprotein (X, beta')4 and the monomeric cytochrome core (n) leads to the hypothesis that the two domains are not tightly associated in the native molecule and might more relative to each other . Their respective mobility is possibly required for the catalytic mechanism . The comparison with previous trypsinolysis studies on the flavocytochrome b2 from Hansenula anomala suggests the presence of two common zones of hypersensitivity to proteases, along the protomeric polypeptide chain, and strongly supports the validity of the triglobular model for both flavocytochromes. Eur J Biochem, 1980 Oct, 111(1), 161 - 9 Cytochrome b-565 in Saccharomyces cerevisiae: use of mutants in the cob- box region of the mitochondrial DNA to study the functional role of this spectral species of cytochrome b . 2 . Relationship between energetic data and cytochrome b-565 content; Chevillotte-Brivet P et al.; A wild-type strain of Saccharomyces cerevisiae and temperature-dependent revertants of isonuclear box mutants partially or completely devoid of cytocheomr b-565, were used to study the role of this cytochrome in oxidative phosphorylation . At the mitochondrial level, the phosphorylating data and the succinate oxidase activity at three different temperatures (16 degrees C, 28 degrees C and 36 degrees C) were measured in these strains showing various cytochrome b-565 contents . It is concluded that this cytochrome b-565 is not in the main pathway of the electron transfer chain . At the optimum growth temperature (28 degrees C), the measurements of the P/O ratio for the wild phenotype strains, with ethanol as substrate, led to the conclusions that two phosphorylation sites of the respiratory chain are functional in these strains . The growth yields for wild phenotype strains and revertants grown in vivo in complex media, with ethanol or galactose as the energy source (at 16 degrees C, 28 degress C and 36 degrees C), were compared with the cytochrome b-565 content . The growth yields showed small variations if compared to the reference strain, when the cytochrome b-565 content was greatly diminished or absent . Thus the ATP production at side II is independent of the cytochrome b-565 content . Cytochrome b-565 does not play an essential role in oxidative phosphorylation. Eur J Biochem, 1980 Oct, 111(1), 151 - 9 Cytochrome b-565 in Saccharomyces cerevisiae: use of mutants in the cob-box region of the mitochondrial DNA to study the functional role of this spectral species of cytochrome b . 1 . Measurements of cytochromes b-562 and b-565 and selection of revertants devoid of cytochrome b-565; Meunier-Lemesle D et al.; In order to study the functional role of the spectral species of cytochrome b-565 observed in mitochondria, genetically manipulated strains of Saccharomyces cerevisiae have been used . Strains have been found which are devoid of cytochrome b-565 under certain conditions and which nevertheless are able to grow on a respirable substrate . Two different methods have been used to determine the cytochrome b-565 content: anaerobic titrations and antimycin-A-induced reduction of cytochrome b-565 . Both yield the same results. J Bacteriol, 1980 Oct, 144(1), 74 - 81 Fluctuation in polyadenylate size and content in exponential- and stationary-phase cells of Saccharomyces cerevisiae; Sogin SJ et al.; Stationary-phase cells of Saccharomyces cerevisiae were found to have a reduced polyadenylate {poly(A)} content as compared with exponential-phase cells . A sizing procedure for poly(A) was devised to distinguish between alternative hypotheses to explain this reduction . Two major size classes of poly(A) were found . The decreased representation of the larger of the two classes accounted for the majority of the poly(A) loss . The remainder of the loss was accounted for by fewer poly(A)-containing sequences . The smaller of the two poly(A) classes was apparently not of mitochondrial origin and may be added transcriptionally. Genetics, 1980 Oct, 96(2), 315 - 20 Precise mapping of the homothallism genes HML and HMR in Saccharomyces cerevisiae; Klar AJ et al.; The HML and HMR loci carry unexpressed copies of MATa and MAT alpha information, and a replica of that information is transposed to MAT during mating-type interchange in Saccharomyces yeasts . A negative control mechanism keeps silent the information located at the HML and HMR loci . We mapped these loci by constructing strains in which these loci are expressed . In these strains, the mating type of the segregants is dependent upon the allele at HML and HMR . This novel approach is independent of their switching function . HML is located on the left arm of chromosome III distal to his4 by about 26.8 centimorgans (cM) . HMR maps on the right arm of the same chromosome distal to thr4 by about 39.8 cM and proximal to MAL2 by about 1.0 cM . The results allow the exact placement of these loci and are in accord with the observations made by Harashima and Oshima (1976). J Bacteriol, 1980 Oct, 144(1), 92 - 6 Immunochemical studies of the mannans of Saccharomyces cerevisiae X2180-1A-5 and Saccharomyces cerevisiae 4484-24D-1 mutant strains, with special reference to their phosphate content; Okubo Y et al.; The mannans from Saccharomyces cerevisiae mutant strains X2180-1A-5 and 4484-24D-1, both of which were shown to contain small amounts of phosphate (less than 0.2%), were fractionated on a column of diethylaminoethyl-Sephadex into five subfractions designated as fractions I to V . These subfractions contain different amounts of phosphate, ranging from 0.03 to 0.09 (strain X2180-1A-5) and from 0.01 to 0.17% (strain 4484-24D-1) . Fractions I to IV from strain X2180-1A-5 showed nearly identical precipitin activities against the homologous anti-whole cell serum, whereas fraction V, containing the largest amount of phosphate and protein among this mannan subfraction series, showed unexpectedly weaker precipitin activity than those of the other fractions . A synthetic mannan consisting or consecutive alpha-1 leads to 6-linked D-mannopyranosyl residues was found to be cross-reactive with all the mannan subfractions of strain X2180-1A-5 against anti-X2180-1A-5 serum . On the other hand, antibody-precipitating activities of the mannan subfractions of the latter strain were proportional to their phosphate content, although the increments of precipitated antibody nitrogen among the subfractions were quite small . However, fraction V of this mannan subfraction series, containing the largest amounts of phosphate and protein, showed lower precipitin activity than did the other four fractions . These findings indicate that mannans containing no phosphate or relatively small amounts of phosphate, such as those investigated in the present study, are less heterogeneous in the densities of the branching moieties than are highly phosphorylated mannans . These findings suggest that the transfer step of mannosyl-1-phosphate into the precursor(s) of the wild-type strain mannans during the biosynthetic process corresponds to the key reaction responsible for the anionic heterogeneity due to the density heterogeneity of the antigenic determinants. Nucleic Acids Res, 1980 Sep 11, 8(17), 3841 - 9 Post-transcriptional modification of the poly(A) length of galactose-1-phosphate uridyl transferase mRNA in Saccharomyces cerevisiae; Saunders CA et al.; Thermal elution poly(U)-Sepharose chromatography was utilized to fractionate yeast mRNA based on poly(A) size . Analysis of the in vitro translation products of the fractionated RNAs in a wheat-embryo cell-free protein synthesis system shows a heterogeneous but equal distribution of these abundant translatable mRNAs in the different poly(A) size classes . By comparing the translational activity of inducible galactose-1-phosphate uridyl transferase mRNA, which can be monitored as a function of age, to contitutive mRNAs, we demonstrate that initially galactose-1-phosphate uridyl transferase mRNA has a uniformly large poly(A) tail which becomes heterogeneous and shorter with age in the cytoplasm . These observations are consistent with the previously observed cytoplasmic poly(A) catabolism in yeast and with cytoplasmic post-transcriptional modification of the poly(A) length of galactose-1-phosphate uridyl transferase mRNA. J Biol Chem, 1980 Sep 10, 255(17), 8019 - 22 The effect of delta-aminolevulinate on catalase T-messenger RNA levels in delta-aminolevulinate synthase-defective mutants of Saccharomyces cerevisiae; Richter K et al.; Total RNA was isolated from mutants of Saccharomyces cerevisiae that lack active delta-aminolevulinate synthase and are therefore defective in heme biosynthesis . The RNAs were translated in the cell-free protein synthesis system from wheat germ, and the catalase T synthesized was isolated by immunoadsorption and polyacrylamide gel electrophoresis in the presence of dodecyl sulfate . Little or no catalase T product was detected with RNA from mutant cells grown in the absence of a heme precursor . As judged from in vitro translational capacity, RNA fractions from mutant cells grown in the presence of delta-aminolevulinate contained at least 10 times more catalase T mRNA than RNA from unsupplemented cells. Genetics, 1980 Sep, 96(1), 137 - 46 Mapping of the proteinase b structural gene PRB1, in Saccharomyces cerevisiae and identification of nonsense alleles within the locus; Zubenko GS et al.; We report the mapping of the structural gene for proteinase B, PRB1 . It is located 1.1 cM proximal to CAN1 on the left arm of chromosome V of Saccharomyces cerevisiae . We have identified 34 amber and 12 ochre mutations among the 126 prb1 mutations in our collection. J Bacteriol, 1980 Sep, 143(3), 1527 - 9 Isolation and properties of an antisuppressor in Saccharomyces cerevisiae specific for an omnipotent suppressor; Liebman SW et al.; A new Mendelian antisuppressor, ASU10, was isolated and shown to reduce the efficiency of the omnipotent yeast suppressor, sup35 . ASU10 had no effect on the other omnipotent suppressor, sup45, or on several amber suppressors. J Bacteriol, 1980 Sep, 143(3), 1403 - 10 Proline: an essential intermediate in arginine degradation in Saccharomyces cerevisiae; Brandriss MC et al.; Results of studies on proline-nonutilizing (Put-) mutants of the yeast Saccharomyces cerevisiae indicate that proline is an essential intermediate in the degradation of arginine . Put- mutants excreted proline when grown on arginine or ornithine as the sole nitrogen source . Yeast cells contained a single enzyme, delta 1-pyrroline-5-carboxylate (P5C) dehydrogenase, which is essential for the complete degradation of both proline and arginine . The sole inducer of this enzyme was found to be proline . P5C dehydrogenase converted P5C to glutamate, but only when the P5C was derived directly from proline . When the P5C was derived from ornithine, it was first converted to proline by the enzyme P5C reductase . Proline was then converted back to P5C and finally to glutamate by the Put enzymes proline oxidase and P5C dehydrogenase. J Bacteriol, 1980 Sep, 143(3), 1384 - 94 Reserve carbohydrate metabolism in Saccharomyces cerevisiae: responses to nutrient limitation; Lillie SH et al.; The amounts of glycogen and trehalose have been measured in cells of a prototrophic diploid yeast strain subjected to a variety of nutrient limitations . Both glycogen and trehalose were accumulated in cells deprived specifically of nirogen, sulfur, or phosphorus, suggesting that reserve carbohydrate accumulation is a general response to nutrient limitation . The patterns of accumulation and utilization of glycogen and trehalose were not identical under these conditions, suggesting that the two carbohydrates may play distinct physiological roles . Glycogen and trehalose were also accumulated by cells undergoing carbon and energy limitation, both during diauxic growth in a relatively poor medium and during the approach to stationary phase in a rich medium . Growth in the rich medium was shown to be carbon or energy limited or both, although the interaction between carbon source limitation and oxygen limitation was complex . In both media, the pattern of glycogen accumulation and utilization was compatible with its serving as a source of energy both during respiratory adaptation and during a subsequent starvation . In contrast, the pattern of trehalose accumulation and utilization seemed compatible only with the latter role . In cultures that were depleting their supplies of exogenous glucose, the accumulation of glycogen began at glucose concentrations well above those sufficient to suppress glycogen accumulation in cultures growing with a constant concentration of exogenous glucose . The mechanism of this effect is not clear, but may involve a response to the rapid rate of change in the glucose concentration. J Bacteriol, 1980 Sep, 143(3), 1179 - 86 Genetic analysis of Saccharomyces cerevisiae transformed by plasmid containing a supressor transfer ribonucleic acid gene; Thomas DY et al.; The behavior in Saccharomyces cerevisiae of plasmid pYTE1, which contains yeast tyrosine-inserting ochre suppressor SUP4.o, a 4-kilobase EcoRI fragment of yeast 2muDNA, and the bacterial plasmid pBR322, has been studied . Selection of yeast transformants was by suppression of multiple ochre mutations . About 10(3) to 10(4) transformants per microgram of pYTE1 dfeoxyribonucleic acid were obtained . The majority of transformants contained both an integrated copy of the SUP4.o gene plus pBR322 deoxyribonucleic acid sequences and autonomously replicating forms of the plasmid . The integrated copy was extremely stable mitotically and meiotically, but the associated nonintegrated copies were lost at meiosis . The chromosomally integrated pBR322 sequences were linked to the SUP4.o gene . The integration site was at the SUP4+ locus . In transformants with only nonintegrated copies of pYTE1, the expression of suppression was reduced, and the plasmid was unstable in mitosis . Plasmid deoxyribonucleic acid preparations from both types of transformant could be used to retransform yeast cells . Plasmid pYTE1 has restriction enzyme sites useful for the high frequency and stable transformation of other genes into yeasts . The potential uses of this plasmid for transformation of other organisms is discussed. J Bacteriol, 1980 Sep, 143(3), 1530 - 3 Cloning of the URA1 gene of Saccharomyces cerevisiae; Guerry-Kopecko P et al.; A 5.7-kilobase segment of Saccharomyces cerevisiae deoxyribonucleic acid which complements both the yeast ura1 and Escherichia coli pyrD mutations in dihydroorotate dehydrogenase has been cloned in plasmid YRp7. Carbohydr Res, 1980 Aug 15, 83(2), 363 - 70 Growth-inhibitory activity of the D-mannan of Saccharomyces cerevisiae X2180-1A-5 mutant strain against mouse-implanted sarcoma 180 and Ehrlich-carcinoma solid tumor; Matsumoto T et al.; The D-mannan of Saccharomyces cerevisiae X2180-1A-5 mutant strain, which possesses a main chain composed of alpha-(1 yields 6) linked D-mannopyranosyl residues and a small proportion of branches composed of alpha-(1 yields 2)- and alpha-(1 yields 3)-linked D-mannopyranosyl residues, showed strong growth-inhibitory activity against mouse-implanted Sarcoma 180 and Ehrlich-carcinoma solid tumor . The observation that the level of this activity was nearly identical with that of the D-mannan of a wild-type strain of bakers' yeast, which possesses a high proportion of branches composed of alpha-(1 yields 2)-and alpha-(1 yields 3)-linked D-mannopyranosyl residues, suggests that the branches are not essential for antitumor activity . The partial acid-degradation products of both D-mannans, the molecular weight of which was one-third of that of each parent D-mannan, had only one half of the antitumor activity of the parent D-mannans . This suggests that molecular size is the most important factor for the differences in acitvity of the polysaccharides of wild and mutant strains. J Bacteriol, 1980 Aug, 143(2), 958 - 65 Properties of polyadenylate-associated ribonucleic acid from Saccharomyces cerevisiae ascospores; Harper JF et al.; Bulk ribonucleic acid (RNA) was isolated from mechanically disrupted ascospores of Saccharomyces cerevisiae . After two passes over an oligo (dT10) cellulose column, the portion which bound, called poly(A)(+), was characterized . It is heterodisperse in size with a mean molecular weight of approximately 4 X 10(5), but contains some species as large as 7 X 10(5) . The base composition is similar to vegetative poly(A)(+) RNA . The polyadenylate segment is also heterogenous in size, ranging from 90 to 20 bases in length, with a peak at approximately 60 nucleotides in length . Pulse-labeling of asci with {3H-methyl}methionine yields two "caps," 7-methyl guanosine-5'-triphosphoryl-5'-adenosine (or guanosine) identical to that found in vegetative poly(A)(+) RNA . The poly(A)(+) RNA in spores is found in polyribosomes which are, on the average, smaller than vegetative ones . Long-term labeling studies indicate that the fraction of poly(A)(+) RNA in spores is similar to that in vegetative cells. J Bacteriol, 1980 Aug, 143(2), 710 - 4 Levels of acid-soluble polyphosphate in growing cultures of Saccharomyces cerevisiae; Solimene R et al.; Short-chain acid-soluble polyphosphates were extracted from growing cultures of Saccharomyces cerevisiae, and the changes in the levels of these compounds were determined . The production of acid-soluble polyphosphates correlated with the mitochondrial activities since it occurred in two bursts in respiration-competent yeast cells and in only one burst in respiration-deficient yeast cells . The possible role of these compounds is discussed. J Bacteriol, 1980 Aug, 143(2), 603 - 12 Alterations in translatable ribonucleic acid after heat shock of Saccharomyces cerevisiae; McAlister L et al.; Changes in populations of translatable messenger ribonucleic acids (mRNA's) after heat shock of Saccharomyces cerevisiae were examined and found to correlate very closely with transient alterations in patterns of in vivo protein synthesis . Initial changes included an increase in translatable species coding for polypeptides synthesized during heat shock; this increase was found to be dependent on transcription but did not require ongoing protein synthesis . A decrease was observed in the level of translatable mRNA's coding for polypeptides whose synthesis was repressed after heat shock . This decrease was much more rapid than can be explained solely by termination of transcription . Requirements for this rapid loss of RNA from the translatable pool included both transcription and an active rna1 gene product but not protein synthesis . After the initial changes in translatable RNA induced by heat shock, the patterns of both in vivo and in vitro translation products began to revert to the preshock levels . This recovery period, unlike the earlier changes, was dependent upon a requisite period of protein synthesis. Genetics, 1980 Aug, 95(4), 855 - 79 Frameshift suppression in Saccharomyces cerevisiae . III . Isolation and genetic properties of group III suppressors; Cummins CM et al.; Suppressors of ICR-induced mutations that exhibit behavior similar to bacterial frameshift suppressors have been identified in the yeast Saccharomyces cerevisiae . The yeast suppressors have been divided into two groups . Previous evidence indicated that suppressors of one group (Group II: SUF1, SUF3, SUF4, SUF5 and SUF6) represent mutations in the structural genes for glycyl-tRNA's . Suppressors of the other group (Group III: SUF2 and SUF7) were less well characterized . Although they suppressed some ICR-revertible mutations, they failed to suppress Group II frameshift mutations . This communication provides a more thorough characterization of the Group III suppressors and describes the isolation and properties of four new suppressors in that group (SUF8, SUF9, SUF10 and suf11).--In our original study, Group III suppressors were isolated as revertants of the Group III mutations his4-712 and his4-713 . All suppressors obtained as ICR-induced revertants of these mutations mapped at the SUF2 locus near the centromere of chromosome III . Suppressors mapping at other loci were obtained in this study by analyzing spontaneous and UV-induced revertants of the Group III mutations . SUF2 and SUF10 suppress both Group III his4 mutations, whereas SUF7, SUF8, SUF9 and suf11 suppress his4-713, but not his4-712 . All of the suppressors except suf11 are dominant in diploids homozygous for his4-713 . The suppressors fail to suppress representative UAA, UAG and UGA nonsense mutations.--SUF9 is linked to the centromere of chromosome VI, and SUF10 is linked to the centromere of chromosome XIV . A triploid mapping procedure was used to determine the chromosome locations of SUF7 and SUF8 . Subsequent standard crosses revealed linkage of SUF7 to cdc5 on chromosome Xiii and linkage of SUF8 to cdc12 and pet3 on chromosome VIII. Genetics, 1980 Aug, 95(4), 833 - 53 Frameshift suppression Saccharomyces cerevisiae . II . Genetic properties of group II suppressors; Culbertson MR et al.; Suppressors of ICR-induced mutations that exhibit behavior similar to bacterial frameshift suppressors have been identified in the yeast Saccharomyces cerevisiae . The yeast suppressors have been divided into two groups . One of these groups (Group II: SUF1, SUF3, SUF4, SUF5 and SUF6) appears to include a set of informational suppressors in which the vehicle of suppression is glycyl-tRNA . Some of the genetic properties of Group II suppressors are described in this communication.--Corevertants of the Group II frameshift mutations his4-519 and leu2-3 have been characterized to determine the spectrum of reversion events induced by the frameshift mutagen ICR-170 . Seventy-three ICR-induced corevertants were analyzed . With the exception of one cerevertant, which carried an allele of SUF1, all carried alleles of SUF3 or SUF5 . SUF1, SUF3, SUF4 and SUF6 were represented among spontaneous and UV-induced corevertants . In the course of these experiments one of the suppressors was mapped . SUF5, the probable structural gene for tRNAGLY1, is located between ade2 and ade9 on chromosome XV.--SUF1, SUF4 and SUF6 have novel properties and comprise a distinct subset of suppressors . Although these suppressors show no genetic linkage to each other, they share several common features including lethality in haploid pairwise combinations, reduced tRNAGLY3 isoacceptor activity and increased efficiency of suppression in strains carrying the cytoplasmically inherited {PSI} element . In addition, strains carrying SUF1, SUF4 or SUF6 are phenotypically unstable and give rise to mitotic Suf+ segments at high frequency . These segregants invariably contain a linked, second-site mutation that maps in or adjacent to the suppressor gene itself . Strains carrying any of these suppressors also give rise to mitotic segregants that exhibit enhanced efficiency of suppression; mutations responsible for this phenotype map at two loci, upf1 and upf2 . These genes show no genetic linkage to any of the group II suppressors.--Methods that permit positive selection have been devised in order to examine large numbers of variants . The importance of these interacting mutants is underscored by their potential utility in studying suppressor function at the molecular level. Mutat Res, 1980 Aug, 72(3), 397 - 404 Hycanthone as a specific frameshift mutagen in Saccharomyces cerevisiae; Lucchini G et al.; Reversion of mutations of different molecular nature was studied after treatment with hycanthone in mild conditions (0.05--0.4 mM, 4 h in the dark, pH 7.2) . The mutagen had a very low reversion activity on 3 missense and 4 nonsense mutations (2 UAA and 2 UAG), although it was very active on 3 frameshift mutations . Our data on intragenic reversion and frameshift suppressors indicate that hycanthone can induce both insertions and deletions. Biochem J, 1980 Jul 15, 190(1), 145 - 56 Regulation of mitochondrial biogenesis . Occurrence of non-functioning components of the mitochondrial respiratory chain in Saccharomyces cerevisiae grown in the presence of proteinase inhibitors: evidence for proteolytic control over assembly of the respiratory chain; Galkin AV et al.; Yeast was grown in glucose- or galactose-containing media without or with proteinase inhibitors, phenylmethanesulphonyl fluoride and pepstatin . Culture growth was practically not affected by these compounds . Yeast growth on glucose in the presence of either phenylmethanesulphonyl fluoride or pepstatin entails accumulation of cytochromes c, c1, b and aa3 to a 25--30% excess above the control by the stationary phase, while cell respiration is unaffected . During growth on galactose the maximal cytochrome content (per unit weight of biomass) is reached in the mid-exponential phase and then decreases by 30--40% towards the stationary phase, while cell respiration remains constant . Addition of phenylmethanesulphonyl fluoride or pepstatin in the mid-exponential phase blocks the decrease in cytochrome levels and has no effect on cell respiration . Mitochondrial populations isolated from stationary-phase control and phenylmethanesulphonyl fluoride-grown cells glucose cultures display identical succinate oxidase and partial-respiratory-chain activities, despite the differences in cytochrome contents . However, the activities of individual respiratory complexes measured after maximal activation are nearly proportional to the amounts of corresponding components . The same situation holds true for mitochondrial populations from mid-exponential-phase, stationary-phase control and stationary-phase inhibitor-grown cells of galactose cultures . The findings suggest that the 'surplus' respiratory-chain components do not participate in electron flow because of the lack of interaction with adjacent carriers. Prikl Biokhim Mikrobiol, 1980 Jul-Aug, 16(4), 528 - 37 {Purification and characterization of beta-fructofuranosidase from yeast Saccharomyces cerevisiae}; Matulaitite EIu et al.; Intracellular invertase was isolated from the yeast Saccharomyces cerevisiae, race XI, and purified by ion-exchange chromatography on DEAE-cellulose and gel-filtration on Sephadex G-200 . The effect of pH, temperature, metal ions, thiolic agents, and EDTA on the enzyme activity and stability was investigated . The enzyme was estimated to have a molecular weight of 270 000 and a carbohydrate content of 20--30% . By disc-electrophoresis and isoelectric focusing the highly purified enzyme was found to be heterogenous . Its molecular forms had isoelectric points at 3.0, 4.0, 4.5, and 4.9. Genetics, 1980 Jul, 95(3), 611 - 30 Ultraviolet mutagenesis studies of {psi}, a cytoplasmic determinant of Saccharomyces cerevisiae; Tuite MF et al.; UV mutagenesis was used to probe the molecular nature of {psi}, a nonmitochondrial cytoplasmic determinant of Saccharomyces cerevisiae involved in the control of nonsense suppression . The UV-induced mutation from {psi+} to {psi-} showed characteristics of forward nuclear gene mutation in terms of frequency, induction kinetics, occurrence of whole and sectored mutant clones and the effect of the stage in the growth cycle on mutation frequency . The involvement of pyrimidine dimers in the premutational lesion giving the {psi-} mutation was demonstrated by photoreactivation . UV-induced damage to the {psi} genetic determinant was shown to be repaired by nuclear-coded repair enzymes that are responsible for the repair of nuclear DNA damage . UV-induced damage to mitochondrial DNA appeared to be, at least partly, under the control of different repair processes . The evidence obtained suggests that the {psi} determinant is DNA. Proc Natl Acad Sci U S A, 1980 Jul, 77(7), 3912 - 6 Isolation and sequence of the gene for actin in Saccharomyces cerevisiae; Ng R et al.; The yeast Saccharomyces cerevisiae is known to contain the highly conserved and unbiquitous protein actin . We have used cloned actin sequences from Dictyostelium discoideum to identify and clone the actin gene in yeast . Hybridization to genomic fragments of yeast DNA suggest that there is a single actin gene in yeast . We have determined the nucleotide sequence of that gene and its flanking regions . The sequence of the gene reveals an intervening sequence of 309 base pairs in the coding sequences at the 5' end of the gene . The existence and location of the intervening sequence was verified by using the dideoxy chain termination technique to determine the sequence at the 5' terminus of the actin mRNA . The similarity of the splice junction sequences in this gene to those found in higher eukaryotes suggests that yeast must possess a similar splicing enzyme. Mutat Res, 1980 Jul, 78(3), 243 - 52 Induction of mitotic recombination by certain hair-dye chemicals in Saccharomyces cerevisiae; Mayer VW et al.; A number of procedures were used to test for the potential of 5 hair-dye chemicals, 4-nitro-o-phenylenediamine, 2-nitro-p-phenylenediamine, m-phenylenediamine 2,4-diaminoanisole sulfate and 2,5-diaminoanisole sulfate, to induce genetic damage in yeast strains D3 and D4 of Saccharomyces cerevisiae . Various plate-test procedures, short-term suspension assays in phosphate buffer and suspension assays with liver enzyme activation all proved to be ineffective for demonstrating genetic effects of these chemicals . Only suspension assays in which the yeast cells were treated with the test chemical under growing conditions for up to 72 h were effective in demonstrating the genetic activity of 4-nitro-o-phenylenediamine and 2,4-diaminoanisole sulfate . The implications of these results for testing of mutagens in yeast systems are discussed along with other supportive evidence from the literature. Eur J Biochem, 1980 Jul, 108(2), 439 - 47 Regulation of compartmentation of amino acid pools in Saccharomyces cerevisiae and its effects on metabolic control; Messenguy F et al.; Compartmentation of intracellular amino acid pools has been studied under various growth conditions in wild-type strains as well as in mutants . Aspartate, glutamate, leucine and isoleucine pools are present in high concentrations in the cytoplasm, while all the other amino acids are more vacuolar . The nature of the nitrogen source for growth, the effectiveness of nitrogen assimilation, the rate of protein synthesis and the presence of high internal basic amino acid pools are important factors in the repartition of amino acid pools between the cytoplasm and the vacuole. J Bacteriol, 1980 Jul, 143(1), 422 - 6 Nitrogen catabolite repression of asparaginase II in Saccharomyces cerevisiae; Dunlop PC et al.; The biosynthesis of asparaginase II in Saccharomyces cerevisiae is subject to strong catabolite repression by a variety of nitrogen compounds . In the present study, asparaginase II synthesis was examined in a wild-type yeast strain and in strains carrying gdhA, gdhCR, or gdhCS mutations . The following effects were observed: (i) In the wild-type strain, the biosynthesis of asparaginase II was strongly repressed when either 10 mM ammonium sulfate or various amino acids (10 mM) served as the source of nitrogen . (ii) In a yeast strain carrying the gdhA mutation, asparaginase II was synthesized at fully derepressed levels when 10 mM ammonium sulfate was the source of nitrogen . When amino acids (10 mM) served as the nitrogen source, asparaginase II synthesis was strongly repressed . (iii) In a strain carrying the gdhCR mutation, the synthesis of asparaginase II was partially (30 to 40%) derepressed when either 10 mM ammonium sulfate or amino acids were present in the medium . (iv) In a yeast strain containing both gdhA and gdhCR mutations, asparaginase II synthesis was fully derepressed when 10 mM ammonium sulfate was the nitrogen source and partially derepressed when 10 mM amino acids were present . (v) Yeast strains carrying the gdhCS mutation were indistinguishable from the wild-type strain with respect to asparaginase II synthesis. Mutat Res, 1980 Jul, 71(2), 193 - 9 Induction of rho- mutations in yeast Saccharomyces cerevisiae by ethanol; Bandas EL et al.; The kinetics of the killing effect of ethanol was studied at 6-30% concentrations . Ploidy of cells, deficiency of the excision-repair system or holding under no-growth conditions did not influence survival . Ethanol at 24% increased, in the wild strain, the number of respiration-deficient cells from a spontaneous level of 0.4% up to nearly half of all survivors . Genetic analysis showed the mitochondrial nature of induced respiration-deficient mutants (or rho-) . The influence of yeast resistance to some antibiotics was studied on rho- mutagenesis, both spontaneous and induced by ethanol . Neomycin-resistant strains were characterized by a significantly lower level of these mutations than were neomycin-sensitive strains. Cancer Res, 1980 Jul, 40(7), 2323 - 9 Effect of tumor promoters on ultraviolet light-induced mutation and mitotic recombination in Saccharomyces cerevisiae; Kunz BA et al.; Recently, it has been suggested that mitotic recombination is involved in tumor promotion . On this basis, one might expect tumor promoters to be recombinagenic . D7 is a diploid strain of yeast in which both mutation and mitotic recombination can be measured . We have used this strain to assay the known tumor promoters, iodoacetate, anthralin, and 12-O-tetradecanoylphorbol-13-acetate, and the cocarcinogen, catechol, for mutagenicity, recombinagenicity, and the ability to enhance ultraviolet light (UV)-induced genetic events . In the absence of preirradiation with UV, iodoacetate was found to be recombinagenic whereas catechol was mutagenic; however, in both cases, the effects were small . Iodoacetate, anthralin, and catechol potentiated UV-induced mitotic crossing-over, aberrant colony formation, and mutation, while catechol also increased UV-induced gene conversion . We were unable to detect any mutagenic or recombinagenic effect of 12-O-tetradecanoyl-phorbol-13-acetate in either whole cells or spheroplasts . Our results do not indicate any consistent correlation between tumor-promoting activity and the ability of an agent to induce mitotic recombination in yeast . However, the ability to potentiate UV-induced mutation and mitotic recombination may reflect the cocarcinogenic activity of certain promoters. Eur J Biochem, 1980 Jul, 108(2), 373 - 7 Two asparagine synthetases in Saccharomyces cerevisiae; Ramos F et al.; In Saccharomyces cerevisiae L-asparagine auxotrophy, resulting from a lack of L-asparagine synthesis, needs simultaneous defects in two genes . This unusual situation is shown to result from the occurrence of two L-asparagine synthetases . The meaning of this duplication remains obscure . The properties of the two enzymes are remarkably similar: both have a molecular weight of 150,000 and they exhibit a slight repression and a similar inhibition by asparagine . Neither one is located in mitochondria and both are probably cytosolic . Their identification so far lies only in their behaviour on ion-exchange chromatography and in the encoding genes. Nucleic Acids Res, 1980 Jun 25, 8(12), 2679 - 89 The 5' terminus of the precursor ribosomal RNA of Saccharomyces cerevisiae; Klemenz R et al.; The 5' terminus of Saccharomyces cereviasiae 35S pre rRNA was mapped on the rDNA using two methods: 1) Suitable restriction endonuclease fragments were hybridized to total high molecular weight RNA and extended with reverse transcriptase to the 5' end of the RNA template . 2) Other restriction fragments spanning the 5' terminus of 35S pre rRNA and radioactively labeled at their ends were hybridized to high molecular weight RNA and the non hybridized nucleic acids were digested with S1 nuclease . On the basis of these experiments, the 5' terminus of 35S pre rRNA was placed approximately 670 nucleotides upstream from the 17S rRNA coding region . The exact position was determined by reverse transcription as above, but in the presence of dideoxyribonucleoside triphosphates, which served as a way of sequencing the 5' terminal region . 35S pre rRNA synthesis is initiated at a site in EcoRI restriction fragment B which is 48 nucleotides upstream from the EcoRI cleavage site in the coding strand. Nucleic Acids Res, 1980 Jun 11, 8(11), 2349 - 63 Virion DNA-independent RNA polymerase from Saccharomyces cerevisiae; Welsh JD et al.; The "killer" plasmid and a larger double-stranded RNA plasmid of yeast exist in intracellular virion particles . Purification of these particles from a diploid killer strain of yeast (grown into stationary growth on ethanol) resulted in co-purification of a DNA-independent RNA polymerase activity . This activity incorporates and requires all four ribonucleoside triphosphates and will not act on deoxyribonucleoside triphosphates . The reaction requires magnesium, is inhibited by sulfhydryl-oxidizing reagents and high concentrations of monovalent cation, but is insensitive to DNase, alpha-amanitin, and actinomycin D . Pyrophosphate inhibits the reaction as does ethidium bromide . Exogenous nucleic acids have no effect on the reaction . The product is mostly single-stranded RNA, some of which is released from the enzymatically active virions. Genetics, 1980 Jun, 95(2), 273 - 88 Isolation and characterization of pso mutants sensitive to photo-addition of psoralen derivatives in Saccharomyces cerevisiae; Henriques JA et al.; We have isolated mutants sensitive to photo-addition of bi-functional and mono-functional derivatives of psoralen in Saccharomyces cerevisiae . Three of these pso mutants were analyzed in detail . They segregate in meiosis like Mendelian genes and complement each other, as well as existing radiation-sensitive (rad and rev) mutants . The study of heterozygous diploid strains (PSO+/pso) indicates that the three pso genes are recessive . The mutant pso1--1 demonstrates a cross-sensitivity to UV and gamma-rays, whereas mutants pso2--1 and pso3--1 are specifically sensitive to photo-addition of psoralen derivatives . The comparison of exponentially growing cells to stationary-phase cells demonstrates that for the three mutants the defect in repair capacity of DNA cross-links and monoadducts concerns G1 and early S-phase cells . The pso2--1 mutant is, however, also defective in G2 repair and loses diploid resistance when it is in the homozygous state.--The block in repair capacity in these novel mutants is discussed in relation to the three other repair pathways known to be involved in the repair of furocoumarins photo-induced lesions in yeast DNA. Mutat Res, 1980 Jun, 78(2), 151 - 7 Petite induction in Saccharomyces cerevisiae by ethidium analogs: distinction between resting and growing cells; Fukunaga M et al.; The importance of specific substituents, especially amino azide groups, for ethidium induction of petites was evaluated in resting and dividing cells of Saccharomyces cerevisiae through the study of a series of ethidium analogs . The structural requirements in resting and growing cells were found to be different, suggesting that at least two mechanisms are responsible for induction . The significance of particular substituents in the induction processes were recognized by: (1) a dependence upon the ethyl substituent at the ring nitrogen in both actively growing and in resting cells; and (2) the implication that amino substituents are important for the effect in dividing cells and especially in resting cells . Photolytic enhancement of petite induction (via a nitrene which forms a covalent linkage to a biological site) was observed for 3 of the azide analogs, which emphasizes the likelihood that metabolic activation of ethidium to a covalent complex is responsible for its effectiveness . Furthermore, these studies indicate that these monoazide analogs should be ideal probes for examining the mitochondrial mutagenic processes. J Cell Biol, 1980 Jun, 85(3), 811 - 22 Mutants of Saccharomyces cerevisiae unresponsive to cell division control by polypeptide mating hormone; Hartwell LH; Temperature-sensitive mutations that produce insensitivity to division arrest by alpha-factor, a mating pheromone, were isolated in an MATa strain of Saccharomyces cerevisiae and shown by complementation studies to difine eight genes . All of these mutations (designated ste) produce sterility at the restrictive temperature in MATa cells, and mutations in seven of the genes produce sterility in MAT alpha cells . In no case was the sterility associated with these mutations coorectible by including wild-type cells of the same mating type in the mating test nor did nay of the mutants inhibit mating of the wild-type cells; the defect appears to be intrinsic to the cell for mutations in each of the genes . Apparently, none of the mutants is defective exclusively in division arrest by alpha-factor, as the sterility of none is suppressed by a temperature-sensitive cdc 28 mutation (the latter imposes division arrest at the correct cell cycle stage for mating) . The mutants were examined for features that are inducible in MATa cells by alpha-factor (agglutinin synthesis as well as division arrest) and for the characteristics that constitutively distinguish MATa from MAT alpha cells (a-factor production, alpha-factor destruction) . ste2 Mutants are defective specifically in the two inducible properties, whereas ste4, 5, 7, 8, 9, 11, and 12 mutants are defective, to varying degrees, in constitutive as well as inducible aspects . Mutations in ste8 and 9 assume a polar budding pattern unlike either MATa or MAT alpha cells but characteristic of MATa/alpha cells . This study defines seven genes that function in two cell types (MATa and alpha) to control the differentiation of cell type and one gene, ste2, that functions exclusively in MATa cells to mediate responsiveness to polypeptide hormone. J Bacteriol, 1980 Jun, 142(3), 808 - 18 Asymmetrical division of Saccharomyces cerevisiae; Lord PG et al.; The unequal division model proposed for budding yeast (L . H . Hartwell and M . W . Unger, J . Cell Biol . 75:422-435, 1977) was tested by bud scar analyses of steady-state exponential batch cultures of Saccharomyces cerevisiae growing at 30 degrees C at 19 different rates, which were obtained by altering the carbon source . The analyses involved counting the number of bud scars, determining the presence or absence of buds on at least 1,000 cells, and independently measuring the doubling times (gamma) by cell number increase . A number of assumptions in the model were tested and found to be in good agreement with the model . Maximum likelihood estimates of daughter cycle time (D), parent cycle time (P), and the budded phase (B) were obtained, and we concluded that asymmetrical division occurred at all growth rates tested (gamma, 75 to 250 min) . D, P, and B are all linearly related to gamma, and D, P, and gamma converge to equality (symmetrical division) at gamma = 65 min . Expressions for the genealogical age distribution for asymmetrically dividing yeast cells were derived . The fraction of daughter cells in steady-state populations is e-alpha P, and the fraction of parent cells of age n (where n is the number of buds that a cell has produced) is (e-alpha P)n-1(1-e-alpha P)2, where alpha = IN2/gamma; thus, the distribution changes with growth rate . The frequency of cells with different numbers of bud scars (i.e., different genealogical ages) was determined for all growth rates, and the observed distribution changed with the growth rate in the manner predicted . In this haploid strain new buds formed adjacent to the previous buds in a regular pattern, but at slower growth rates the pattern was more irregular . The median volume of the cells and the volume at start in the cell cycle both increased at faster growth rates . The implications of these findings for the control of the cell cycle are discussed. J Bacteriol, 1980 Jun, 142(3), 791 - 9 Regulatory mutations affecting ornithine decarboxylase activity in Saccharomyces cerevisiae; Cohn MS et al.; We isolated several strains of Saccharomyces cerevisiae containing mutations mapping at a single chromosomal gene (spe10); these strains are defective in the decarboxylation of L-ornithine to form putrescine and consequently do not synthesize spermidine and spermine . The growth of one of these mutants was completely eliminated in a polyamine-deficient medium; the growth rate was restored to normal if putrescine, spermidine, or spermine was added . spe10 is not linked to spe2 (adenosylmethionine decarboxylase) or spe3 (putrescine aminopropyltransferase {spermidine synthease}) . spe 10 is probably a regulatory gene rather than the structural gene for ornithine decarboxylase, since we isolated two different mutations which bypassed spe10 mutants; these were spe4, an unliked recessive mutation, and spe40, a dominant mutation linked to spe10 . Both spe4 and spe40 mutants exhibited a deficiency of spermidine aminopropyltransferase (spermine synthase), but not of putrescine aminopropyltransferase . This suggests that ornithine decarboxylase activity is negatively controlled by the presence of spermidine aminopropyltransferase. J Bacteriol, 1980 Jun, 142(3), 747 - 54 Biosynthesis of phosphoinositol-containing sphingolipids from phosphatidylinositol by a membrane preparation from Saccharomyces cerevisiae; Becker GW et al.; Incubation of membranes prepared from Saccharomyces cerevisiae with {32P}phosphatidyl{3H}inositol resulted in the transfer of both labels to two products which were characterized as two species of inositolphosphoceramide, differing in the ceramide portion of the molecule . The products were characterized on the basis of stability in mild alkali, mobility on silica gel-impregnated paper, chromatography on silicic acid columns, and release of inositol phosphate upon base hydrolysis . The reaction did not require the addition of metals, nor was it inhibited by ethylenediaminetetraacetic acid . The detergents Triton X-100 and Tween 20 provided little, if any, stimulation . At relatively high concentrations of phosphatidylinositol (1 to 4 mM), the in vitro rate was about 20% of the in vivo rate . Although ceramide was a logical substrate, the reaction could not be greatly stimulated by the addition of ceramides containing mono- and dihydroxy fatty acids . In addition, incubation of yeast membranes with {32P}phosphatidylinositol gave rise to a product that was chromatographically indistinguishable from the major yeast phosphosphingolipid, mannose-(inositol-P)2 ceramide. J Bacteriol, 1980 Jun, 142(3), 852 - 8 Inhibition and activation of mannan synthesis in Saccharomyces cerevisiae spheroplast lysates; Harrington CR et al.; Mannan synthetase activity in spheroplast lysates prepared from Saccharomyces cerevisiae was measured by following the incorporation of {14C}mannose from guanosine 5'-diphosphate-{14C}mannose into material precipitable with cold 0.3 M perchloric acid . When enzyme activity was assayed at high concentrations of spheroplast lysate protein (10 mg/ml) in the presence of 7.5 mM MnCl2, a severe inhibition was observed . This inhibition could be relieved by preincubation of the spheroplast lysate at 4 degrees C for 16 to 32 h before assay, by repeated freezing and thawing of the spheroplast lysate, or by the omission of MnCl2 from assay mixtures . The addition of ethylenediaminetetraacetic acid or monovalent cations removed inhibition in the presence of Mn2+ . No similar inhibition was observed when a washed membrane fraction was substituted for spheroplast lysate as the source of mannan synthetase . The supernatant fluid obtained by centrifuging spheroplast lysate at 100,000 x g, when added to assay mixtures containing either spheroplast lysate preincubated at 4 degrees C or washed membrane fraction, also caused inhibition of enzyme activity . This inhibition required 7.5 mM MnCl2 and was destroyed by heating the supernatant fluid at 60 degrees C for 10 min, or by trypsin treatment at 30 degrees C . These results indicate the existence of a protein inhibitor of mannan synthesis whose inhibitory activity in spheroplast lysates may be modulated by preincubation at low temperature or by varying the available Mn2+ concentration. Biochem J, 1980 Jun 1, 187(3), 843 - 9 Mechanistic studies of carboxypeptidase Y from Saccharomyces cerevisiae . pH and pD profiles and inactivation at low pH (pD) values; Chang WT et al.; Steady-state kinetics of carboxypeptidase Y, a proteinase from yeast, were studied by using the reaction of 4-nitrophenyl trimethylacetate as a probe . The pH profile of kcat . is sigmoidal in H2O-based buffers for the carboxypeptidase Y-catalysed hydrolysis of this ester (kcat . referring to the rate of deacylation of trimethylacetyl-carboxypeptidase Y) . The corresponding pD profile in 2H2O is doubly sigmoidal, with inflexions at pD approximately 3.8 and approximately 6.8 . The ionization of pKDapp . approximately 3.8 is caused by a rapid inactivation in 2H2O media by a process that is only slowly reversed on transfer to pH 7.00 phosphate buffer in H2O . The corresponding inactivation in H2O-based buffers of low pH is considerably slower (approximately 30-fold), follows a first-order rate-dependence and is very strongly pH-dependent, indicating some form of co-operative change in enzyme tertiary structure. Biochim Biophys Acta, 1980 May 22, 629(3), 445 - 54 Metabolic relationship between invertase and acid phosphatase isoenzymes in Saccharomyces cerevisiae; Rodriguez L et al.; Repressed cells of Saccharomyces cerevisiae, subjected to inhibition of both RNA and protein synthesis, showed a pattern of membrane-bound and cytosol acid phosphatase to the external enzyme which seemed to be linked through a precursor-product relationship . Gel exclusion chromatography did not indicate clear differences between the isoenzymes . Moreover, centrifugation experiments in CsCl and precipitation with concanavalin A suggested that there were no acid phosphatase molecules devoid of carbohydrate . Membrane-bound invertase displayed a molecular weight and a carbohydrate to protein ratio smaller than those of the exocellular enzyme . The values of molecular weight and buoyant density of the membrane-bound enzyme were closer to those found for the cytosol invertase . The stability of the level of the soluble invertase detected in the cytoplasm under derepression conditions, or after RNA or protein synthesis inhibition was found to be only apparent and represented the result of an equilibrium between synthesis and degradation. Biochemistry, 1980 May 13, 19(10), 2236 - 40 High mobility group proteins of Saccharomyces cerevisiae; Weber S et al.; The yeast Saccharomyces cerevisiae contains four proteins having amino acid compositions typical of the high mobility group (HMG) proteins . Three of these are eluted from chromatin by 0.35 M NaCl; one is not, but it is eluted by 0.25 N HCl . It follows that HMGs cannot, in general, be defined by extractability criteria . Gel mobilities and amino acid compositions indicate that yeast and animal HMGs have diverged markedly. Proc Natl Acad Sci U S A, 1980 May, 77(5), 2546 - 50 Structure of a split yeast gene: complete nucleotide sequence of the actin gene in Saccharomyces cerevisiae; Gallwitz D et al.; The complete nucleotide sequence of the actin gene from Saccharomyces cerevisiae has been determined . The coding region is interrupted by a 304-base-pair intervening sequence that is located within the triplet coding for amino acid 4 . DNA sequences of the intron-exon junctions are similar to those found in higher eukaryotes and can be aligned such that the intron starts with the dinucleotide 5'-G-T-3' and ends with 5'-A-G-3' . Regions fo homology within the sequences upstream from the initiation codon and those following the termination codon have been detected between the yeast iso-1-cytochrome c gene and the actin gene . As deduced from the nucleotide sequence, yeast actin has 374 amino acid residues . Its primary structure, especially the NH2-terminal third of the protein, is highly conserved during evolution. Eur J Biochem, 1980 May, 106(2), 661 - 5 Binding and inhibitory effect of 2-heptyl-4-hydroxyquinoline-N-oxide in the presence of ubiquinone-3 in Saccharomyces cerevisiae; Burger G; 1 . 2-Heptyl-4-hydroxyquinoline-N-oxide (HpHOQnO) binds to oxidized mitochondria of Saccharomyces cerevisiae with a dissociation constant of 5 x 10(-8) M and with a ratio of 1 mol per mol cytochrome b . 2 . After addition of 171 micro M ubiquinone-3 to oxidized mitochondria, 0.3 mol HpHOQnO bind to 1 mol cytochrome b . The binding strength of the inhibitor is not essentially affected . 3 . Reduction of mitochondria with succinate results in a strong decrease of the HpHOQnO binding . The dissociation constant could not be calculated on the basis of the applied method . 4 . On the basis of the inhibitory effect of HpHOQnO on reduced mitochondria, a dissociation constant of 5 x 10(-6) M is calculated . 5 . The respiratory electron flow to oxygen is about 100 times as sensitive to HpHOQnO as the electron flow to cytochrome c . 6 . Ubiquinone-3 reverses the inhibition by HpHOQnO and stimulates the electron flow . 7 . The different influence of ubiquinone-3 in binding and in inhibition experiments is discussed as a result of redox conditions. Cell, 1980 May, 20(1), 199 - 206 Mosaic organization of a mitochondrial gene: evidence from double mutants in the cytochrome b region of Saccharomyces cerevisiae; Alexander NJ et al.; The region coding for apocytochrome b in the mitochondrial genome of Saccharomyces cerevisiae is believed to exhibit a mosaic organization, consisting in certain strains of five exons and four introns . This model can be tested by the use of double mutants, each containing two physically, genetically and phenotypically defined mit- lesions in cis, (that is, in the same mitochondrial chromosome) . Such mutants have been constructed, and the phenotypes of several examples of each of the four possible classes--exon-exon, exon-intron (downstream), intron (upstream)-exon and intron-intron--have been examined . Our results have shown that upstream mutations are always epistatic to downstream ones for polypeptide products, and that regulation of expression of cytochrome oxidase subunit I by introns is epistatic regardless of position . These findings have provided an independent verification of the mosaic model, and also suggest that at least the majority of novel polypeptides accumulating in intron mutants are hybrid products that contain sequences of the wild-type polypeptide. Experientia, 1980 Apr 15, 36(4), 385 - 6 Active transport of dimethialium in Saccharomyces cerevisiae; Iwashima A et al.; Dimethialium, a derivative of thiamine which has a methyl group in place of hydroxyethyl group at the t-position of the thiazole moiety, was found to be accumulated in nonproliferating cells of Saccharomyces cerevisiae by the same transport mechanism for thiamine . The results strongly support the supposition that thiamine as well as dimethialium can be transported and accumulated without obligatory phosphorylation in yeast cells, since dimethialium is not phosphorylated by yeast thiamine pyrophosphokinase. J Biol Chem, 1980 Apr 10, 255(7), 3080 - 5 Purification and characterization of a Saccharomyces cerevisiae exoribonuclease which yields 5'-mononucleotides by a 5' leads to 3' mode of hydrolysis; Stevens A; An exoribonuclease producing 5'-mononucleotides has been purified from ribosomes of Saccharomyces cerevisiae . The enzyme has a broad pH optimum around 8.0, requires divalent cation, and is stimulated by monovalent cation with the cation and degree of stimulation being dependent on the substrate used . With either poly(A) or rRNA as substrate, the enzyme has a processive mode of hydrolysis . The oligonucleotides, (pA)3-5, are hydrolyzed by the enzyme, and the hydrolysis is dependent on a 5'-phosphate end group . Phosphorylation of the 3' end has little effect on the rate of hydrolysis . With {3H}poly(A) or {3H}rRNA, labeled differentially at the 5' termini, a more rapid release of 5'-terminal label can be shown, providing evidence that the enzyme hydrolyzes in a 5' leads to 3' direction . Further evidence for a 5' leads to 3' mode of hydrolysis is provided by a study of the products of the hydrolysis of {3H}(pA)5 labeled at the 5' termini with 32P . No 32P label is found in (pA)2 which accumulates as an intermediate. Nature, 1980 Apr 3, 284(5755), 426 - 30 Unequal crossing over in the ribosomal DNA of Saccharomyces cerevisiae; Szostak JW et al.; Unequal sister chromatid exchanges occur at the ribosomal DNA locus of yeast during mitotic growth . The frequency of unequal crossing over, as measured by the deletion or duplication of an inserted genetic marker (LEU2), is sufficient to maintain the sequence homogeneity of the rDNA repeat units. Mol Gen Genet, 1980 Apr, 178(1), 69 - 76 The metabolic prop