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Zidovudine, Lamivudine, and Abacavir Have Different Effects on Resting Cells Infected with Human Immunodeficiency Virus In Vitro. Jesús Saavedra-Lozano, 2004.We have previously described an in vitro model for the evaluation of the effects of different immunomodulatory agents and immunotoxins (ITs) on cells latently infected with human immunodeficiency virus (HIV) . We demonstrated that latently infected, replication-competent cells can be generated in vitro after eliminating CD25+ cells with an IT . Thus, by selectively killing the productively infected cells with an anti-CD25 IT we can generate a population of latently infected cells . CD25– cells generated in this manner were treated with nucleoside analog reverse transcriptase inhibitors and subsequently activated with phytohemagglutinin in the presence of the drugs . The antiviral activities of zidovudine (ZDV), lamivudine (3TC), and abacavir (ABC) were evaluated by using this model . 3TC and ABC demonstrated significant activity in decreasing HIV production from recently infected resting cells following their activation, whereas the effect of ZDV was more modest . These results suggest that the differences in antiviral activity of nucleoside analogs on resting cells should be considered when designing drug combinations for the treatment of HIV infection . The model presented here offers a convenient alternative for evaluating the mechanism of action of new antiretroviral agents (J . Saavedra, C . Johnson, J . Koester, M . St . Claire, E . Vitteta, O . Ramilo, 37th Intersci . Conf . Antimicrob . Agents Chemother., abstr . I-59, 1997) . An N-Terminally Truncated RpoS (  S) Protein in Escherichia coli Is Active In Vivo and Exhibits Normal Environmental Regulation Even in the Absence of rpoS Transcriptional and Translational Control Signals.K. Rajkumari, 2002.RpoS ( S) in Escherichia coli is a stationary-phase-specific primary sigma factor of RNA polymerase which is 330 amino acids long and belongs to the eubacterial
70 family of proteins . Conserved domain 1.1 at the N-terminal end of
70 has been shown to be essential for RNA polymerase function, and its deletion has been shown to result in a dominant-lethal phenotype . We now report that a
S variant with a deletion of its N-terminal 50 amino acids (S 1-50), when expressed in vivo either from a chromosomal rpoS::IS10 allele (in rho mutant strains) or from a plasmid-borne arabinose-inducible promoter, is as proficient as the wild type in directing transcription from the proU P1 promoter; at three other
S-dependent promoters that were tested (osmY, katE, and csiD), the truncated protein exhibited a three- to sevenfold reduced range of activities . Catabolite repression at the csiD promoter (which requires both
S and cyclic AMP [cAMP]-cAMP receptor protein for its activity) was also preserved in the strain expressing
S1-50 . The intracellular content of
S1-50 was regulated by culture variables such as growth phase, osmolarity, and temperature in the same manner as that described earlier for
S, even when the truncated protein was expressed from a template that possessed neither the transcriptional nor the translational control elements of wild-type rpoS . Our results indicate that, unlike that in
70, the N-terminal domain in
S may not be essential for the protein to function as a sigma factor in vivo . Furthermore, our results suggest that the induction of
S-specific promoters in stationary phase and during growth under conditions of high osmolarity or low temperature is mediated primarily through the regulation of
S protein degradation .
Real-Time Imaging of Fluorescent Flagellar Filaments of Rhizobium lupini H13-3: Flagellar Rotation and pH-Induced Polymorphic Transitions. Birgit Scharf, 2002.The soil bacterium Rhizobium lupini H13-3 has complex right-handed flagellar filaments with unusual ridged, grooved surfaces . Clockwise (CW) rotation propels the cells forward, and course changes (tumbling) result from changes in filament speed instead of the more common change in direction of rotation . In view of these novelties, fluorescence labeling was used to analyze the behavior of single flagellar filaments during swimming and tumbling, leading to a model for directional changes in R . lupini . Also, flagellar filaments were investigated for helical conformational changes, which have not been previously shown for complex filaments . During full-speed CW rotation, the flagellar filaments form a propulsive bundle that pushes the cell on a straight path . Tumbling is caused by asynchronous deceleration and stops of individual filaments, resulting in dissociation of the propulsive bundle . R . lupini tumbles were not accompanied by helical conformational changes as are tumbles in other organisms including enteric bacteria . However, when pH was experimentally changed, four different polymorphic forms were observed . At a physiological pH of 7, normal flagellar helices were characterized by a pitch angle of 30°, a pitch of 1.36 µm, and a helical diameter of 0.50 µm . As pH increased from 9 to 11, the helices transformed from normal to semicoiled to straight . As pH decreased from 5 to 3, the helices transformed from normal to curly to straight . Transient conformational changes were also noted at high viscosity, suggesting that the R . lupini flagellar filament may adapt to high loads in viscous environments (soil) by assuming hydrodynamically favorable conformations . Expression Levels of the Yeast Alcohol Acetyltransferase Genes ATF1, Lg-ATF1, and ATF2 Control the Formation of a Broad Range of Volatile Esters. Kevin J. Verstrepen, 2003.Volatile aroma-active esters are responsible for the fruity character of fermented alcoholic beverages such as beer and wine . Esters are produced by fermenting yeast cells in an enzyme-catalyzed intracellular reaction . In order to investigate and compare the roles of the known Saccharomyces cerevisiae alcohol acetyltransferases, Atf1p, Atf2p and Lg-Atf1p, in volatile ester production, the respective genes were either deleted or overexpressed in a laboratory strain and a commercial brewing strain . Subsequently, the ester formation of the transformants was monitored by headspace gas chromatography and gas chromatography combined with mass spectroscopy (GC-MS) . Analysis of the fermentation products confirmed that the expression levels of ATF1 and ATF2 greatly affect the production of ethyl acetate and isoamyl acetate . GC-MS analysis revealed that Atf1p and Atf2p are also responsible for the formation of a broad range of less volatile esters, such as propyl acetate, isobutyl acetate, pentyl acetate, hexyl acetate, heptyl acetate, octyl acetate, and phenyl ethyl acetate . With respect to the esters analyzed in this study, Atf2p seemed to play only a minor role compared to Atf1p . The atf1  atf2 double deletion strain did not form any isoamyl acetate, showing that together, Atf1p and Atf2p are responsible for the total cellular isoamyl alcohol acetyltransferase activity . However, the double deletion strain still produced considerable amounts of certain other esters, such as ethyl acetate (50% of the wild-type strain), propyl acetate (50%), and isobutyl acetate (40%), which provides evidence for the existence of additional, as-yet-unknown ester synthases in the yeast proteome . Interestingly, overexpression of different alleles of ATF1 and ATF2 led to different ester production rates, indicating that differences in the aroma profiles of yeast strains may be partially due to mutations in their ATF genes .
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