Carboxypetidase S from yeast: regulation of its activity during vegetative growth and differentiation

Cis and trans-acting regulatory elements required for regulation of the CPS1 gene in Saccharomyces cerevisiae

To clarify the transcriptional regulation by nutrient limitation of the gene encoding carboxypeptidase yscS in Saccharomyces cerevisiae (CPS1), we performed an analysis of its 5' noncoding region. In deletion experiments a sequence located between positions -644 and -591 was found to be responsible for transcriptional repression of the CPS1 gene in yeast cells grown on rich nitrogen sources. Furthermore, a 162 bp fragment spanning positions -644 to -482 of the promoter of the CPS1 gene repressed gene expression when placed 3' to the upstream activation sequence (UAS) of the heterologous gene CYC1. A fragment containing this putative upstream repression sequence (URS) was shown specifically to bind protein from a yeast extract as demonstrated by gel retardation experiments. Although a sequence mediating the control of gene expression by GCN4 was found within the URS element, the GCN4 gene product is not required for DNA-binding activity. In addition, at least three other upstream activation UASs responsible for the activation of CPS1 expression by glucose under nitrogen starvation conditions were found to be located between positions -673 and -644, -482 and -353, and -243 and -186, respectively. The putative mechanism of the nitrogen limitation-dependent regulation of CPS1 expression via these regulatory elements is discussed.

Control of Saccharomyces cerevisiae carboxypeptidase S (CPS1) gene expression under nutrient limitation

Expression of the vacuolar carboxypeptidase S (CPS1) gene in Saccharomyces cerevisiae is regulated by the availability of nutrients. Enzyme production is sensitive to nitrogen catabolite repression; i.e. the presence of ammonium ions maintains expression of the gene at a low level. Transfer of ammonium-glucose pre-grown cells to a medium deprived of nitrogen causes a drastic increase in CPS1 RNA level provided that a readily usable carbon source, such as glucose or fructose, is available to the cells. Derepression of the gene by nitrogen limitation is cycloheximide-insensitive. Neither glycerol, ethanol, acetate nor galactose support derepression of CPS1 expression under nitrogen starvation conditions. Non-metabolizable sugar analogs (2-deoxyglucose, 6-methyl-glucose or glucosamine) do not allow derepression of CPS1, showing that the process is energy-dependent. Production of carboxypeptidase yscS also increases several-fold when ammonium-pregrown cells are transferred to media containing glucose and a non-readily metabolizable nitrogen source such as proline, leucine, valine or leucyl-glycine. Analysis of CPS1 expression in RAS2+ (high cAMP) and ras2 mutant (low cAMP) strains and in cells grown at low temperature (23 degrees C) and in heat-shocked cells (38 degrees C) shows that steady-state levels of CPS1 mRNA are not controlled by a low cAMP level-signalling pathway.

Molecular cloning and sequencing of genomic DNA encoding yeast vacuolar carboxypeptidase yscS

A Saccharomyces cerevisiae genomic DNA encoding vacuolar carboxypeptidase yscS was cloned from a yeast YEp13 library by complementation of the previously characterized mutation cps1-1 [(1981) J. Bacteriol. 147, 418-426], by means of staining carboxypeptidase activity in yeast colonies. The nucleotide sequence of the cloned gene was determined. The open reading frame of CPS1 consists of 576 codons and therefore encodes a protein of 64961 molecular weight. A stretch of 19 residues near the N-terminus of the deduced polypeptide sequence contains characteristics common to known hydrophobic leader sequences. CPS1 was determined by DNA blot analysis to be a single copy gene located on chromosome X. The cloned fragment was used to identify a 2.1 kb mRNA. A transcriptional activation of CPS1 occurs when cells grow on a substrate of carboxy-peptidase yscS as sole nitrogen source.

Carboxypeptidase S- and carboxypeptidase Y-deficient mutants of Saccharomyces cerevisiae

A new carboxypeptidase (carboxypeptidase S) was found in a Saccharomyces cerevisiae strain lacking carboxypeptidase Y (D. H. Wolf and U. Weiser, Eur. J. Biochem. 73:553-556, 1977). Mutants devoid of carboxypeptidase S activity were isolated from a mutant strain that was also deficient in carboxypeptidase Y. Four mutants were analyzed in detail and fell into one complementation group. The defect segregated 2:2 in meiotic tetrads. Gene dosage experiments indicated that the mutation might reside in the structural gene of carboxypeptidase S. The absence of both enzymes, carboxypeptidases Y and S, did not affect mitotic growth. Ascopore formation was only slightly affected by the absence of both carboxypeptidases. Protein degradation under conditions of nutrient deprivation and under sporulation conditions showed no obvious alteration in the absence of carboxypeptidases Y and S. When a proteinase B mutation, which led to the absence of proteinase B activity and resulted in the partial reduction of sporulation, was introduced into a mutant lacking both carboxypeptidases, the ability of diploid cells to sporulate was nearly completely lost. Mutants lacking both carboxypeptidases were unable to grow on the dipeptide benzyloxycarbonylglycyl-l-leucine as a sole nitrogen source, which indicates an additional function for carboxypeptidases Y and S in supplying nutrients from exogenous peptides. Catabolite inactivation of fructose-1,6-bisphosphatase, cytoplasmic malate dehydrogenase, and phosphoenolpyruvate carboxykinase and inactivation of nicotin-amide adenine dinucleotide phosphate-dependent, glutamate dehydrogenase, events which have been proposed to involve proteolysis in vivo, were not dependent on the presence of carboxypeptidase Y and S. In a mutant lacking both carboxypeptidases, four new proteolytic enzymes with carboxypeptidase activity were detected.

Asparaginase II of Saccharomyces cerevisiae: inactivation during the transition to stationary phase

Asparaginase II (L-asparagine amidohydrolase, EC 3.5.1.1) activity of cells from stationary phase cultures of Saccharomyces cerevisiae is very low. When these cells are inoculated into minimal medium, asparaginase II specific activity rises rapidly and reaches a maximum after 9-10 h. During the next 2.5-3 h, a rapid decrease in asparaginase II specific activity occurs. The enzyme does not appear to be secreted into the medium or to be reabsorbed into the cell. Addition of protease inhibitors at the time of maximum activity partially or totally prevents the loss of asparaginase II. L-1-Tosylamide-2-phenylethyl chloromethyl ketone decreases the rate of loss. The sulfhydryl reagents p-hydroxymercuribenzoate and iodoacetamide inhibit the loss of asparaginase II. However, addition of EDTA causes a further increase in activity. This increase is due to de novo protein synthesis. The effect of EDTA can be reversed by the addition of Zn2+. The most likely explanation for the rapid loss of asparaginase II is proteolytic degradation by a Zn2+-dependent, thiol protease or peptidase.