MUTATIONAL ANALYSIS OF THE SACCHAROMYCES-CEREVISIAE GENERAL REGULATORY FACTOR CP1

The Saccharomyces cerevisiae general regulatory factor CP1, a helix-lo op-helix protein that binds the centromere DNA element I (CDEI) of yea st centromeres, is required in yeast for optimal centromere function a nd for methionine prototrophy. Mutant alleles of CEP1, the gene encodi ng CP1, were generated by linker insertion, 5'- and 3'-deletion, and r andom mutagenesis and assayed for DNA binding activity and their abili ty to confer CP1 function when expressed in yeast. A heterologous CDEI -binding protein, TFEB, was also tested for CP1 function. The results suggested that DNA binding is required for both biological functions o f CP1 but is not sufficient. A direct and quantitative correlation was observed between the chromosome loss and nutritional (i.e., Met) phen otypes of strains carrying loss of function alleles, but qualitatively the chromosome loss phenotype was more sensitive to decreased CP1 exp ression. The data are consistent with a model in which CP1 performs th e same general chromatin-related function at centromeres and MET gene promoters and is normally present in functional excess.