Genetic properties of mutations at the PEP4 locus in Saccharomyces cerevisiae

Yeast cells that inherit mutations at the PEP4 locus exhibit a pronounced phenotypic lag in the expression of the mutant phenotype imparted by these mutations. This lag appears to extend to all of the enzymes that are affected by the pep4-3 mutation. For at least two of the enzymatic activities, phenotypic lag shows mitotic cosegregation. Phenotypic lag is found for meiotic progeny and for mitotic segregants from heterokaryons. The phenotypic lag in the expression of the carboxypeptidase Y deficiency is abolished by nonsense mutations in either PRC1, the structural gene for carboxypeptidase Y, or PRB1, the structural gene for proteinase B. Models to explain these observations are proposed.