Immunochemical studies on catabolite inactivation of phosphoenolpyruvate carboxykinase in Saccharomyces cerevisiae

Analysis of proteinase A function in yeast

Yeast mutants lacking proteinase A were isolated. One of these mutants (Hb I) is characterized in detail. The mutation called pra1 segregates 2:2 in meiotic tetrads indicating a single gene mutation. No anti-(proteinase A) cross-reacting material can be detected. Diploids heterozygous for pra1 show gene dosage. Thus, it appears that PRA1 might be the structural gene for proteinase A. Results obtained with this mutant show that proteinase A is not a vital component of the vegetative cell cycle. The mutant exhibits normal mitotic growth under rich and poor growth conditions and shows normal mating. Enzymes subject to carbon catabolite inactivation and inactivation of NADP-dependent glutamate dehydrogenase, processes which were proposed to be of proteolytic nature, are not affected by the absence of proteinase A. However, protein degradation under sporulation conditions is about 30% reduced in proteinase A mutant cells. The differentiation process of sporulation is also disturbed leading to a 40% reduced sporulation frequency in mutant cells.

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.