Mitochondria-Mediated Programmed Cell Death in Saccharomyces cerevisiae Induced by Betulinic Acid Is Accelerated by the Deletion of PEP4 Gene

In this work, using Saccharomyces cerevisiae as a model, we showed that BetA could inhibitcell proliferation and lead to lethal cytotoxicity accompanying programmed cell death (PCD).Interestingly, it was found that vacuolar protease Pep4p played a pivotal role in BetA‐induced S.cerevisiae PCD. The presence of Pep4p reduced the damage of BetA‐induced cells. This work impliedthat BetA may induce cell death of S. cerevisiae through mitochondria‐mediated PCD, and thedeletion of Pep4 gene possibly accelerated the effect of PCD. The present investigation provided thepreliminary research for the complicated mechanism of BetA‐induced cell PCD regulated by vacularprotease Pep4p and lay the foundation for understanding of the Pep4p protein in an animal model.

A Cell-Free Assay Allows Reconstitution of Vps33p-Dependent Transport to the Yeast Vacuole/Lysosome

We report a cell-free system that measures transport-coupled maturation of carboxypeptidase Y (CPY). Yeast spheroplasts are lysed by extrusion through polycarbonate filters. After differential centrifugation, a 125,000-g pellet is enriched for radiolabeled proCPY and is used as “donor” membranes. A 15,000-g pellet, harvested from nonradiolabeled cells and enriched for vacuoles, is used as “acceptor” membranes. When these membranes are incubated together with ATP and cytosolic extracts, ∼50% of the radiolabeled proCPY is processed to mature CPY. Maturation was inhibited by dilution of donor and acceptor membranes during incubation, showed a 15-min lag period, and was temperature sensitive. Efficient proCPY maturation was possible when donor membranes were from a yeast strain deleted for the PEP4 gene (which encodes the principal CPY processing enzyme, proteinase A) and acceptor membranes from a PEP4 yeast strain, indicating intercompartmental transfer. Cytosol made from a yeast strain deleted for the VPS33 gene was less efficient at driving transport. Moreover, antibodies against Vps33p (a Sec1 homologue) and Vam3p (a Q-SNARE) inhibited transport >90%. Cytosolic extracts from yeast cells overexpressing Vps33p restored transport to antibody-inhibited assays. This cell-free system has allowed the demonstration of reconstituted intercompartmental transport coupled to the function of a VPS gene product.

PEP4 gene of Saccharomyces cerevisiae encodes proteinase A, a vacuolar enzyme required for processing of vacuolar precursors

The proteinase A structural gene of Saccharomyces cerevisiae was cloned by using an immunological screening procedure that allows detection of yeast cells which are aberrantly secreting vacuolar proteins (J. H. Rothman, C. P. Hunter, L. A. Valls, and T. H. Stevens, Proc. Natl. Acad. Sci. USA, 83:3248-3252, 1986). A second cloned gene was obtained on a multicopy plasmid by complementation of a pep4-3 mutation. The nucleotide sequences of these two genes were determined independently and were found to be identical. The predicted amino acid sequence of the cloned gene suggests that proteinase A is synthesized as a 405-amino-acid precursor which is proteolytically converted to the 329-amino-acid mature enzyme. Proteinase A shows substantial homology to mammalian aspartyl proteases, such as pepsin, renin, and cathepsin D. The similarities may reflect not only analogous functions but also similar processing and intracellular targeting mechanisms for the two proteins. The cloned proteinase A structural gene, even when it is carried on a single-copy plasmid, complements the deficiency in several vacuolar hydrolase activities that is observed in a pep4 mutant. A strain carrying a deletion in the genomic copy of the gene fails to complement a pep4 mutant of the opposite mating type. Genetic linkage data demonstrate that integrated copies of the cloned proteinase A structural gene map to the PEP4 locus. Thus, the PEP4 gene encodes a vacuolar aspartyl protease, proteinase A, that is required for the in vivo processing of a number of vacuolar zymogens.

The PEP4 gene encodes an aspartyl protease implicated in the posttranslational regulation of Saccharomyces cerevisiae vacuolar hydrolases.

pep4 mutants of Saccharomyces cerevisiae accumulate inactive precursors of vacuolar hydrolases. The PEP4 gene was isolated from a genomic DNA library by complementation of the pep4-3 mutation. Deletion analysis localized the complementing activity to a 1.5-kilobase pair EcoRI-XhoI restriction enzyme fragment. This fragment was used to identify an 1,800-nucleotide mRNA capable of directing the synthesis of a 44,000-dalton polypeptide. Southern blot analysis of yeast genomic DNA showed that the PEP4 gene is unique; however, several related sequences exist in yeasts. Tetrad analysis and mitotic recombination experiments localized the PEP4 gene proximal to GAL4 on chromosome XVI. Analysis of the DNA sequence indicated that PEP4 encodes a polypeptide with extensive homology to the aspartyl protease family. A comparison of the PEP4 predicted amino acid sequence with the yeast protease A protein sequence revealed that the two genes are, in fact, identical (see also Ammerer et al., Mol. Cell. Biol. 6:2490-2499, 1986). Based on our observations, we propose a model whereby inactive precursor molecules produced from the PEP4 gene self-activate within the yeast vacuole and subsequently activate other vacuolar hydrolases.

PEP4 gene of Saccharomyces cerevisiae encodes proteinase A, a vacuolar enzyme required for processing of vacuolar precursors.

The proteinase A structural gene of Saccharomyces cerevisiae was cloned by using an immunological screening procedure that allows detection of yeast cells which are aberrantly secreting vacuolar proteins (J. H. Rothman, C. P. Hunter, L. A. Valls, and T. H. Stevens, Proc. Natl. Acad. Sci. USA, 83:3248-3252, 1986). A second cloned gene was obtained on a multicopy plasmid by complementation of a pep4-3 mutation. The nucleotide sequences of these two genes were determined independently and were found to be identical. The predicted amino acid sequence of the cloned gene suggests that proteinase A is synthesized as a 405-amino-acid precursor which is proteolytically converted to the 329-amino-acid mature enzyme. Proteinase A shows substantial homology to mammalian aspartyl proteases, such as pepsin, renin, and cathepsin D. The similarities may reflect not only analogous functions but also similar processing and intracellular targeting mechanisms for the two proteins. The cloned proteinase A structural gene, even when it is carried on a single-copy plasmid, complements the deficiency in several vacuolar hydrolase activities that is observed in a pep4 mutant. A strain carrying a deletion in the genomic copy of the gene fails to complement a pep4 mutant of the opposite mating type. Genetic linkage data demonstrate that integrated copies of the cloned proteinase A structural gene map to the PEP4 locus. Thus, the PEP4 gene encodes a vacuolar aspartyl protease, proteinase A, that is required for the in vivo processing of a number of vacuolar zymogens.

The PEP4 gene encodes an aspartyl protease implicated in the posttranslational regulation of Saccharomyces cerevisiae vacuolar hydrolases

pep4 mutants of Saccharomyces cerevisiae accumulate inactive precursors of vacuolar hydrolases. The PEP4 gene was isolated from a genomic DNA library by complementation of the pep4-3 mutation. Deletion analysis localized the complementing activity to a 1.5-kilobase pair EcoRI-XhoI restriction enzyme fragment. This fragment was used to identify an 1,800-nucleotide mRNA capable of directing the synthesis of a 44,000-dalton polypeptide. Southern blot analysis of yeast genomic DNA showed that the PEP4 gene is unique; however, several related sequences exist in yeasts. Tetrad analysis and mitotic recombination experiments localized the PEP4 gene proximal to GAL4 on chromosome XVI. Analysis of the DNA sequence indicated that PEP4 encodes a polypeptide with extensive homology to the aspartyl protease family. A comparison of the PEP4 predicted amino acid sequence with the yeast protease A protein sequence revealed that the two genes are, in fact, identical (see also Ammerer et al., Mol. Cell. Biol. 6:2490-2499, 1986). Based on our observations, we propose a model whereby inactive precursor molecules produced from the PEP4 gene self-activate within the yeast vacuole and subsequently activate other vacuolar hydrolases.

PEP4 GENE FUNCTION IS REQUIRED FOR EXPRESSION OF SEVERAL VACUOLAR HYDROLASES IN SACCHAROMYCES CEREVISIAE

ABSTRACT The pep4-3 mutation results in a 90-95% reduction in the levels of five vacuolar hydrolases in yeast, including proteinases A and B, carboxypeptidase Y, RNase(s) and the repressible alkaline phosphatase. The mutation is without effect on two secreted glycoproteins, on an enzyme of the vacuolar membrane, and on a proteinase located outside of the vacuole. Mutations at the PEP4 locus exhibit a dosage effect on the levels of some, but not all, of the enzymes whose expression requires the function of the gene.