Abstract
Mutants deficient in the vacuolar (lysosomal) endopeptidases proteinase yscA and proteinase yscB of the yeast Saccharomyces cerevisiae exhibit a drastically reduced protein degradation rate under nutritional stress conditions. The differentiation process of sporulation is considerably disturbed by the absence of the two endopeptidases. Also under vegetative growth conditions and under conditions of false protein synthesis, the two vacuolar endopeptidases exhibit some effect on protein degradation, which is, however, much less pronounced as found under starvation conditions. Proteinase yscA deficiency leads to rapid cell death when glucose-grown cells starve for nitrogen or other nutrients. Whereas overall protein degradation is affected in the endopeptidase mutants, degradation of two distinct false proteins analyzed is not altered in the absence of proteinase yscA and proteinase yscB. Also catabolite inactivation and degradation of fructose-1,6-bisphosphatase is not affected to a greater extent in the endopeptidase-deficient strains.
Highlights
THEJOURNAL OF BIOLOGICACHLEMISTRY0 1989 by The American Society for Biochemistryand MolecularBiology, Inc. Vol 264, No 27, Issue of September 25, pp. 16037-16045,1969 Printed in U.S A
Mutants deficient in the vacuolar endo- others [24,25,26] have isolated and characterized mutants of the peptidases proteinase yscA and proteinase yscB of the yeast Saccharomyces cerevisiae exhibit a drastically reduced protein degradation rate under nutritional stress conditions
Whereas overall protein degradation isaffected in the endopeptidase mutants, degradation of Impact of the Vacuolar Endopeptidases Proteinase yscA and ProteinaseyscB on Protein Degradation in Starvingand Growing Cells-The level of the two vacuolar proteinases yscA and yscB is rather low under conditions of vegetative growth on glucose [39] and increases considerably under conditions of poor carbon supply and nitrogen starvation [29,39,40].When two distinct false proteins analyzed is not altered in diploid MATalMATa yeast cells are transferred to such nuthe absence of proteinase yscA and proteinase yscB. tritional stress conditions, catabolite inactivation and degradation of fruc- they undergo the differentiation process of sporulation [41]
Summary
0 1989 by The American Society for Biochemistryand MolecularBiology, Inc. Vol 264, No 27, Issue of September 25, pp. 16037-16045,1969 Printed in U.S A. A variety of hydrolases, among them two endopeptidases, in the activities of proteinase yscA and proteinase yscB (pralproteinase yscA and proteinase yscB, and five exopeptidases, 1prbl-1) exhibit only a degradation rate of 0.46%/h during carboxypeptidases yscY and yscS, aminopeptidases yscI and the first 8 h on sporulation medium under the same condiyscCo as well as dipeptidyl aminopeptidase yscV, have been tions, which amountsto 14% of wild type (Fig. 1) This shown to be associated with this cellular organelle [1,2,5,6]. The double mutant pral-1 prbl-1 carrying deficiencies in both proteinasaectivities, yscA and yscB, shows with a rate of 15%of wild type a considerably lower degradation rate than thpep mutant This phenomenon might be explained by the fact that even though the pep mutant does notcarrymatureproteinase yscB, it contains an inta4c2t -kDa precursor of proteinase yscB, which has recently been shown to be capable of degrading protein (ll),whereas the pral-1 prbl-1 double mutant harbors mutated, inactive proteinase yscB. We investigated whether the drastic decrease of the degradation capacity of 85% in pral-1 prbl-1 double
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