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  • 1
    ISSN: 1432-0983
    Keywords: Heat shock ; Thermotolerance ; Ploidy ; Yeast
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary The resistance of Saccharomyces cerevisiae to inactivation by DNA damaging agents has long been known to be affected by cell ploidy. Resistance is greater for diploid than for haploid cells, but exhibits decreases for further increases in ploidy beyond diploid. In this study S. cerevisiae cells whose genomes differ only in their ploidy were employed to investigate how ploidy directly influences resistance to thermal killing. In virtually all species resistance to thermal killing is a cellular property that is elevated by heat shock and other agents that induce the heat shock response. We therefore investigated how ploidy affected the thermal killing of S. cerevisiae cells both before and after elevation of thermotolerance by means of a 40 min 25 °C to 38 °C heat shock. Without such induction of thermotolerance there was negligible effect of ploidy on thermal killing. In contrast in the heat shocked cultures there was an appreciable decrease in thermotolerance as ploidy increased. This difference indicates that the lethal thermal damage in the thermotolerance induced cultures is not totally equivalent to that in cells not given a prior heat shock, and that gene expression changes after heat shock result in a ploidy effect on heat tolerance which is absent from cells in which the heat shock response has not been induced.
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  • 2
    ISSN: 1432-0983
    Keywords: Saccharomyces cerevisiae ; Aminoacyl-tRNA synthetase mutant ; PGK overexpression ; In vivo misreading
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary The hts1.1 temperature-sensitive histidinyl-tRNA synthetase mutation enables Saccharomyces cerevisiae to be starved for His-tRNAHis by upshift to the non-permissive temperature of 38°C. If yeast behaves similarly to bacterial and mammalian cells, this lack of His-tRNAHis should greatly enhance misreading at histidine codons (CAU/CAC) by Gln-tRNAGln, resulting in substitution of the neutral amino acid glutamine in place of histidine, a basic amino acid. Such misreading causes the isoelectric point (pI) of proteins to shift to lower values, and is readily detectable as “stuttering” on two-dimensional (2D) protein gels. By gel analysis of pulse-labelled proteins of hts1.1 yeast cells that were overexpressing phosphoglycerate kinase (PGK), our study sought to detect this specific translational error in PGK protein. It was not detected by this relatively sensitive technique, indicating that missense errors due to glutamine insertion at histidine codons do not occur in yeast at the readily-detectable level found in bacterial and mammalian cells.
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  • 3
    ISSN: 1432-0983
    Keywords: Saccharomyces cerevisiae ; Episomal plasmid ; Copy number control ; Plasmid maintenance ; Glycolytic enzyme levels
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary This study demonstrates how varying the promoter strength of an essential gene on a yeast 2μORI-STB YEp multicopy vector can influence vector copy levels. A phosphoglycerate kinase gene (PGK) on this plasmid was made essential for fermentative growth by transformation into a pgk - yeast strain. When in these PGK- transformants the requirement for PGK expression was the sole selective criterion for plasmid maintenance, PGK promoter activity was inversely related to vector copy levels. Plasmids with an efficiently-transcribed PGK gene were maintained at approximately one copy per cell, whereas those lacking the UAS that normally directs high basal PGK transcription levels were present at up to 10–15 copies. All cultures of these PGK+ transformants contained only a low proportion of pgk - cells. Since mitotic loss of the plasmid arrests growth through loss of a functional PGK allele, PGK confers high stability to the YEp vector in such a pgk - genetic background. In this system YEp vector levels are probably influenced by PGK transcription because high expression of PGK is needed in rapid fermentative growth. Remarkably, low plasmid PGK promoter activity caused PGK mRNA levels slightly higher than those found in yeast with normal PGK regulation. A higher plasmid copy number is therefore not the only factor counteracting the effects of low PGK transcription, and it is possible that PGK mRNA becomes more stable in response to inefficient PGK transcription.
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  • 4
    ISSN: 1432-0983
    Keywords: Yeast ; Heterologous gene expression ; Sulfolobus ; Hyperthermophile phosphoglycerate kinase ; Archaea
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The gene encoding phosphoglycerate kinase (PGK) from the ArchaeonSulfolobus solfataricus, an organism growing optimally at 87°C, was inserted into a yeast expression vector under the control of the galactose-inducibleGAL1 yeast promoter. This vector was then transformed into apgk::TRP1 yeast mutant, a strain inhibited for growth on galactose or glucose due to its lack of PGK enzyme. Slow-growing transformants were obtained on galactose plates at 37°C, but not 28°C. These transformants contained low levels of transcripts of the heterologous gene and low amounts of thermostable PGK activity. Weak expression of the hyperthermophile gene in yeast a mesophile, therefore enabled complementation of the yeastpgk defect at 37°C but not at 28°C.
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  • 5
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] Hsp90 (heat shock protein of 90 kDa) is a ubiquitous molecular chaperone responsible for the assembly and regulation of many eukaryotic signalling systems and is an emerging target for rational chemotherapy of many cancers. Although the structures of isolated domains of Hsp90 ...
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  • 6
    ISSN: 1546-1696
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: [Auszug] We have found an influence of cellular ubiquitin levels over the secretion of human leucocyte elastase inhibitor (elafin) by Saccharomyces cerevisiae. Inactivation of the UBI4 polyubiquitin gene reduced elafin secretion 3 to 4-fold. Conversely ubiquitin overexpression, by galactose induction of an ...
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  • 7
    ISSN: 1072-8368
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Medicine
    Notes: [Auszug] Hsp90 is a highly specific chaperone for many signal transduction proteins, including steroid hormone receptors and a broad range of protein kinases. The crystal structure of the N-terminal domain of the yeast Hsp90 reveals a dimeric structure based on a highly twisted sixteen stranded ...
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  • 8
    ISSN: 1574-6968
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Abstract A temperature-sensitive mutant of Saccharomyces cerevisiae has been isolated which accumulates a large pool of trehalose-6-phosphate when shifted to temperatures above 34°C nonpermissive for growth. This indicates that its defect is in the second enzyme of trehalose biosynthesis, the hydrolase that converts trehalose-6-phosphate to trehalose. Trehalose is made continouosly when yeast is growing on high glucose or when it is starved for a nitrogen source, and accumulates as cells enter the stationary phase. Revertants of the mutant able to grow at 37°C arise spontaneously and no longer accumulate trehalose-6-phosphate at this temperature. Also the kinetics of trehalose-6-phosphate accumulation in the mutant following a 25–37°C shift resemble the kinetics of inhibition of RNA and protein synthesis. It is probable therefore that accumulation of high levels of this metabolic intermediate is inhibitory to growth.
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  • 9
    ISSN: 1574-6968
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Abstract The HSP70 genes of eukaryotes show up to 50% nucleotide sequence homology to the dnaK gene of Escherichia coli. This extreme structure conservation implies conservation of a function that may be needed by all cells, suggesting that other bacteria may have sequences related to HSP70 and dnaK. Amongst other functions, HSP70-like proteins may act to limit thermal protein denaturation. In this study DNA isolated from thermophilic archaebacteria (from the family Desulfurococcus) and thermophilic eubacteria (from the families Bacillus and Thermus) was probed with sequences from a heat shock inducible HSP70 gene of the yeast Saccharomyces cerevisiae. Hybridization was detected under conditions of low stringency, indicating the existence of HSP70-related sequences in the thermophilic bacteria studied.
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  • 10
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: A factor influencing resistances of food spoilage microbes to sorbate and benzoate is whether these organisms are able to catalyse the degradation of these preservative compounds. Several fungi metabolize benzoic acid by the β-ketoadipate pathway, involving the hydroxylation of benzoate to 4-hydroxybenzoate. Saccharomyces cerevisiae is unable to use benzoate as a sole carbon source, apparently through the lack of benzoate-4-hydroxylase activity. However a single gene from the food spoilage yeast Zygosaccharomyces bailii, heterologously expressed in S. cerevisiae cells, can enable growth of the latter on benzoate, sorbate and phenylalanine. Although this ZbYME2 gene is essential for benzoate utilization by Z. bailii, its ZbYme2p product has little homology to other fungal benzoate-4-hydroxylases studied to date, all of which appear to be microsomal cytochrome P450s. Instead, ZbYme2p has strong similarity to the matrix domain of the S. cerevisiae mitochondrial protein Yme2p/Rna12p/Prp12p and, when expressed as a functional fusion to green fluorescent protein in S. cerevisiae growing on benzoate, is largely localized to mitochondria. The phenotypes associated with loss of the native Yme2p from S. cerevisiae, mostly apparent in yme1,yme2 cells, may relate to increased detrimental effects of endogenous oxidative stress. Heterologous expression of ZbYME2 complements these phenotypes, yet it also confers a potential for weak acid preservative catabolism that the native S. cerevisiae Yme2p is unable to provide. Benzoate utilization by S. cerevisiae expressing ZbYME2 requires a functional mitochondrial respiratory chain, but not the native Yme1p and Yme2p of the mitochondrion.
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