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  • 1
    ISSN: 1432-0983
    Keywords: Saccharomyces cerevisiae ; Omnipotent suppression ; Nonsense suppression ; SUP45
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Using a plasmid-based termination-read-through assay, the sal4-2 conditional-lethal (temperature-sensitive) allele of the SUP45 (SAL4) gene was shown to enhance the efficiency of the weak ochre suppressor tRNA SUQ5 some 10-fold at 30°C. Additionally, this allele increased the suppressor efficiency of SRM2-2, a weak tRNAGln ochre suppressor, indicating that the allosuppressor phenotype is not SUQ5-specific. A sup + sal4-2 strain also showed a temperature-dependent omnipotent suppressor phenotype, enhancing readthrough of all three termination codons. Combining the sal4-2 allele with an efficient tRNA nonsense suppressor (SUP4) increased the temperature-sensitivity of that strain, indicating that enhanced nonsense suppressor levels contribute to the conditional-lethality conferred by the sal4-2 allele. However, UGA suppression levels in a sup + sal4-2 strain following a shift to the non-permissive temperature reached a maximum significantly below that exhibited by a non-temperature sensitive SUP4 suppressor strain. Enhanced nonsense suppression may not therefore be the primary cause of the conditional-lethality of this allele. These data indicate a role for Sup45p in translation termination, and possibly in an additional, as yet unidentified, cellular process.
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  • 2
    ISSN: 1432-0983
    Keywords: Saccharomyces cerevisiae ; Allosuppressor ; Translation ; Fidelity
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Allosuppressor (sal) mutations enhance the efficiency of the yeast ochre suppressor SUQ5 and define five unlinked loci, SALT-SALS. A number of sal4 mutants were isolated and found to have pleiotropic, allele;specific phenotypes, including hypersensitivity in vivo to paromomycin and other antibiotics that stimulate translational errors in yeast. To examine further the nature of the SAL4 gene product, the wild type SAL4 gene was isolated by complementation of a conditional lethal allele sal4-2, and demonstrated to be a single copy gene encoding a single 1.6 kb transcript. Restriction mapping and DNA hybridisation analysis were used to demonstrate that the SAL4 gene is identical to the previously identified omnipotent suppressor gene SUP45 (SUPT). Our results implicate the SAL4 gene product as playing a major role in maintaining translational accuracy in yeast.
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  • 3
    ISSN: 1432-0983
    Keywords: Candida albicans ; Termination ; Suppressor tRNA ; Translation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Clinical isolates of the dimorphic fungus Candida albicans encode a tRNA that, in a cell-free translation system prepared from the yeast Saccharomyces cerevisiae, efficiently translates the amber (UAG) termination codon. Unusually, the efficiency of this UAG read-through in the heterologous cell-free system is not further enhanced by polyamines. The suppressor tRNA is also able to efficiently translate the UAG codon in the rabbit reticulocyte cell-free system and with efficiencies approaching 100% in a homologous (C. albicans) cell-free system. That the suppressor tRNA is nuclear-encoded is demonstrated by the lack of activity in purified C. albicans mitochondrial tRNAs. Finally, UAG suppressor tRNA activity is also demonstrated in three other pathogenic Candida species, C. parapsilosis, C. guillermondii and C. tropicalis. These results suggest that some, but not all, Candida species have evolved an unusual nuclear genetic code in which UAG is used as a sense codon.
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  • 4
    Electronic Resource
    Electronic Resource
    [s.l.] : Nature Publishing Group
    Nature 370 (1994), S. 327-328 
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] CELL biologists often look to the yeast Saccharomyces cerevisiae as a convenient model system in which to study universal problems of eukaryotic cellular physiology and gene regulation. In a reversal of this situation, three recent papers1"3 look to work on mammalian neurodegener-ative disease to ...
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  • 5
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Molecular microbiology 3 (1989), S. 0 
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: The synthesis of heat-shock proteins can be triggered by a variety of stress-inducing conditions. Here we show that translational misreading caused by growth in the presence of the aminoglycoside antibiotic paromomycin will induce the heat-shock response in the yeast Saccharomyces cerevisiae. This was demonstrated (i) by the acquisition of thermotolerance, and (ii) by elevated levels of expression of the heat-shock protein, hsp70. In addition, transcription of the ubiquitin gene (UBI4) was increased in paromomycin-grown cells. Control experiments with the protein synthesis inhibitor cycloheximide (which does not induce translational misreading) demonstrated that the response was not due to inhibition of protein synthesis per se. These observations strongly suggest that the synthesis of abnormally high levels of aberrant proteins is the trigger of the heat-shock response in this simple eukaryote.
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  • 6
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Yeast 4 (1988), S. 159-178 
    ISSN: 0749-503X
    Keywords: Life and Medical Sciences ; Genetics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology
    Additional Material: 11 Ill.
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  • 7
    ISSN: 1432-1432
    Keywords: Elongation factor 3 ; EF-3 ; Translation ; Ribosomal protein ; Fungal protein synthesis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Fungi appear to be unique in their requirement for a third soluble translation elongation factor. This factor, designated elongation factor 3 (EF-3), exhibits ribosome-dependent ATPase and GTPase activities that are not intrinsic to the fungal ribosome but are nevertheless essential for translation elongation in vivo. The EF-3 polypeptide has been identified in a wide range of fungal species and the gene encoding EF-3 (YEF3) has been isolated from four fungal species (Saccharomyces cerevisiae, Candida albicans, Candida guillermondii, andPneumocystis carinii). Computer-assisted analysis of the predictedS. cerevisiae EF-3 amino acid sequence was used to identify several potential functional domains; two ATP binding/catalytic domains conserved with equivalent domains in members of the ATP-Binding Cassette (ABC) family of proteins, an aminoterminal region showing significant similarity to theE. coli S5 ribosomal protein, and regions of predicted interaction with rRNA, tRNA, and mRNA. Furthermore, EF-3 was also found to display amino acid similarity to myosin proteins whose cellular function is to provide the motive force of muscle. The identification of these regions provides clues to both the evolution and function of EF-3. The predicted functional regions are conserved among all known fungal EF-3 proteins and a recently described homologue encoded by the Chlorella virus CVK2. We propose that EF-3 may play a role in the ribosomal optimization of the accuracy of fungal protein synthesis by altering the conformation and activity of a ribosomal “accuracy center,” which is equivalent to the S4-S5-S12 ribosomal protein accuracy center domain of theE. coli ribosome. Furthermore, we suggest that EF-3 represents an evolving ribosomal protein with properties analogous to the intrinsic ATPase activities of higher eukaryotic ribosomes, which has wider implications for the evolutionary divergence of fungi from other eukaryotes.
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  • 8
    ISSN: 1432-1432
    Keywords: Elongation factor 3 ; EF-3 ; Translation ; Ribosomal protein ; Fungal protein synthesis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Fungi appear to be unique in their requirement for a third soluble translation elongation factor. This factor, designated elongation factor 3 (EF-3), exhibits ribosome-dependent ATPase and GTPase activities that are not intrinsic to the fungal ribosome but are nevertheless essential for translation elongation in vivo. The EF-3 polypeptide has been identified in a wide range of fungal species and the gene encoding EF-3 (YEF3) has been isolated from four fungal species (Saccharomyces cerevisiae, Candida albicans, Candida guillermondii, and Pneumocystis carinii). Computer-assisted analysis of the predicted S. cerevisiae EF-3 amino acid sequence was used to identify several potential functional domains; two ATP binding/catalytic domains conserved with equivalent domains in members of the ATP-Binding Cassette (ABC) family of proteins, an aminoterminal region showing significant similarity to the E. coli S5 ribosomal protein, and regions of predicted interaction with rRNA, tRNA, and mRNA. Furthermore, EF-3 was also found to display amino acid similarity to myosin proteins whose cellular function is to provide the motive force of muscle. The identification of these regions provides clues to both the evolution and function of EF-3. The predicted functional regions are conserved among all known fungal EF-3 proteins and a recently described homologue encoded by the Chlorella virus CVK2. We propose that EF-3 may play a role in the ribosomal optimization of the accuracy of fungal protein synthesis by altering the conformation and activity of a ribosomal “accuracy center,” which is equivalent to the S4-S5-S12 ribosomal protein accuracy center domain of the E. coli ribosome. Furthermore, we suggest that EF-3 represents an evolving ribosomal protein with properties analogous to the intrinsic ATPase activities of higher eukaryotic ribosomes, which has wider implications for the evolutionary divergence of fungi from other eukaryotes.
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  • 9
    ISSN: 1572-9699
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
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