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Query: UMLS:C0038187 (starvation)
 24,951 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

For determination of the physiological role and mechanism of vacuolar proteolysis in the yeast Saccharomyces cerevisiae, mutant cells lacking proteinase A, B, and carboxypeptidase Y were transferred from a nutrient medium to a synthetic medium devoid of various nutrients and morphological changes of their vacuoles were investigated. After incubation for 1 h in nutrient-deficient media, a few spherical bodies appeared in the vacuoles and moved actively by Brownian movement. These bodies gradually increased in number and after 3 h they filled the vacuoles almost completely. During their accumulation, the volume of the vacuolar compartment also increased. Electron microscopic examination showed that these bodies were surrounded by a unit membrane which appeared thinner than any other intracellular membrane. The contents of the bodies were morphologically indistinguishable from the cytosol; these bodies contained cytoplasmic ribosomes, RER, mitochondria, lipid granules and glycogen granules, and the density of the cytoplasmic ribosomes in the bodies was almost the same as that of ribosomes in the cytosol. The diameter of the bodies ranged from 400 to 900 nm. Vacuoles that had accumulated these bodies were prepared by a modification of the method of Ohsumi and Anraku (Ohsumi, Y., and Y. Anraku. 1981. J. Biol. Chem. 256:2079-2082). The isolated vacuoles contained ribosomes and showed latent activity of the cytosolic enzyme glucose-6-phosphate dehydrogenase. These results suggest that these bodies sequestered the cytosol in the vacuoles. We named these spherical bodies "autophagic bodies." Accumulation of autophagic bodies in the vacuoles was induced not only by nitrogen starvation, but also by depletion of nutrients such as carbon and single amino acids that caused cessation of the cell cycle. Genetic analysis revealed that the accumulation of autophagic bodies in the vacuoles was the result of lack of the PRB1 product proteinase B, and disruption of the PRB1 gene confirmed this result. In the presence of PMSF, wild-type cells accumulated autophagic bodies in the vacuoles under nutrient-deficient conditions in the same manner as did multiple protease-deficient mutants or cells with a disrupted PRB1 gene. As the autophagic bodies disappeared rapidly after removal of PMSF from cultures of normal cells, they must be an intermediate in the normal autophagic process. This is the first report that nutrient-deficient conditions induce extensive autophagic degradation of cytosolic components in the vacuoles of yeast cells.
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PMID:Autophagy in yeast demonstrated with proteinase-deficient mutants and conditions for its induction. 140 May 75

The Saccharomyces cerevisiae genes FAS1 and FAS2 encoding the beta and alpha subunit of yeast fatty acid synthetase (FAS), respectively, were individually deleted by one-step gene disruption. Northern blot analysis of RNA from the resulting fas null allele mutants indicated that deletion of FAS2 did not influence the transcription of FAS1, while FAS2 transcription was significantly reduced in the delta fas1 strain. These data suggest an activating role of subunit beta on FAS2 gene expression or, alternatively, a repression of FAS2 by an excess of its own gene product. Compared to the intact alpha 6 beta 6 complex, the individual FAS subunits synthesized in the delta fas1 or delta fas2 strains exhibit a considerably increased sensitivity towards the proteinases present in the yeast cell homogenate. Using yeast mutants specifically defective in the vacuolar proteinases yscA (PRA1/ PEP4 gene product) and/or yscB (PRB1 gene product), it was shown that in vitro, subunit alpha is efficiently degraded by proteinase yscA while for degradation of subunit beta, the combined action of proteinases yscA and yscB is necessary. In vivo, besides the vacuolar proteinases, an additional proteolytic activity specifically affecting free FAS subunit alpha becomes increasingly apparent in cells entering the stationary growth phase. In contrast, under similar conditions uncomplexed FAS subunit beta is stable in strains lacking the vacuolar proteinases yscA and yscB. The reduced FAS subunit levels, at the stationary phase, were independent of the corresponding FAS transcript concentrations. Thus, differential degradation pathways are obviously removing an excess of either FAS subunit, at least under starvation conditions. A combination of both regulation of FAS gene expression and proteolysis of free FAS polypeptides may therefore explain the equimolar amounts of both FAS subunits observed in yeast wild-type cells.
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PMID:Differential proteolytic sensitivity of yeast fatty acid synthetase subunits alpha and beta contributing to a balanced ratio of both fatty acid synthetase components. 173 46

The activation process of vacuolar proteinases in the yeast Saccharomyces cerevisiae via precursor maturation is initiated by the PRA1/PEP4 gene product, proteinase yscA. Chromosomal deletion of the PRA1/PEP4 locus leads to accumulation of inactive pro-proteinases in the vacuole. Nine active-site mutations of proteinase yscA have been constructed in vitro. All these mutations lead to the expression of proteinase yscA species in vivo that are inactive against the in vitro substrate hemoglobin and the in vivo substrates pro-proteinase yscB and pro-carboxypeptidase yscY. However, three active-site mutations in proteinase yscA sustained the precursor maturation of proteinase yscB and carboxypeptidase yscY after exchange of the genomic wild-type allele with the respective proteinase yscA mutant alleles. In contrast to yeast strains deleted in proteinase yscA, the respective mutants carry out all cellular functions that rely on a proteolytically active vacuole. This wild-type behaviour of proteinase yscA mutant cells is dependent on the presence of active proteinase yscB. Proteinase yscA and proteinase yscB are equally able to fulfil essential cellular functions. For instance, either proteinase is able to maintain viability under starvation. However, mature proteinase yscB is not stable in the absence of proteinase yscA. The wild-type-like conformation of proteolytically inactive mutant proteinase yscA proteins stabilizes mature proteinase yscB and thus enables continuous maturation of pro-proteinase yscB by active proteinase yscB. After inhibition of the proteolytic activity of proteinase yscB in these proteinase yscA mutants with phenylmethysulfonyl fluoride or deletion of the PRB1 gene, maturation of all zymogens investigated in the vacuole, including the proteinase yscA mutant proteins, is blocked. The proteolytic activities of the vacuole in such a strain can be regained, however, by introduction of a wild-type proteinase yscA gene allowing subsequent autocatalytic maturation of wild-type pro-proteinase yscA. This indicates that an initial self-activation process of proteinase yscA is necessary for the activation of vacuolar zymogens.
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PMID:Biogenesis of the yeast vacuole (lysosome). The use of active-site mutants of proteinase yscA to determine the necessity of the enzyme for vacuolar proteinase maturation and proteinase yscB stability. 762 61

We previously reported a genetic analysis of the growth-inhibitory effect caused by the overexpression of the Aspergillus oryzae rntA gene, encoding RNase T1 (Ribonuclease T1), in Saccharomyces cerevisiae. Subsequently, rns (ribonuclease T1 sensitive) mutants with mutations in the rns1 (DSL1), rns2 (UMP1), and rns3 (SEC17) genes, were identified. In the present study, rns4 (VPS32/SNF7) gene mutation was identified by complementation of tunicamycin sensitivity. While the rns4 mutant exhibited sensitivity to ambient stress conditions (200 mM CaCl(2), 1M NaCl and pH 8.0), genome-wide expression analysis revealed a similar pattern of genes up-regulated as was observed under nitrogen depletion condition by Gasch et al. [Mol. Biol. Cell 11 (2000) 4241]. Notably, the genes participating in autophagy (ATG4 and ATG8), the genes encoding a vacuolar protease (PRB1), vacuolar protease inhibitors (PAI3, PBI2 and TFS1) and YHR138c (a PBI2 homolog) were up-regulated in the rns4 mutant. Interestingly, the RNase T1*-GFP fusion protein (*inactive form) expressed in the rns4 mutant strain localized at the ER and vacuole under both stress or no-stress conditions. In contrast, the RNase T1*-GFP fusion protein expressed in the wild-type strain could not be detected under no-stress conditions, however, a stress-dependent localization of the fusion protein was observed at the vacuole. Since, the rns4 mutant exhibited a partial starvation-like response in spite of a rich ambient environment, leading to transportation of the secretory protein to the vacuole and accumulation in the endoplasmic reticulum, the present findings implicate a novel role for Rns4/Vps32 in proper response and adaptation to ambient conditions.
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PMID:Identification and characterization of rns4/vps32 mutation in the RNase T1 expression-sensitive strain of Saccharomyces cerevisiae: Evidence for altered ambient response resulting in transportation of the secretory protein to vacuoles. 1592 8