A novel mutation occurring in the PHO80 gene suppresses the PHO4c mutations of Saccharomyces cerevisiae.

We have isolated suppressors of a PHO4c (a positive regulator) mutant which normally confers weak constitutivity for acid phosphatase production on the Saccharomyces cell. One dominant suppressor (PHO80-2) was found to be an allele of PHO80 (a negative regulator) that changes G to A, resulting in substitution of isoleucine for methionine 42 of the Pho80 protein. Substitution of valine (PHO80-3) or leucine (PHO80-4) for the same methionine by site-directed mutagenesis also suppressed PHOc. Suppression by PHO80-2) did show some allele specificity. From these results we were able to delimit the region of PHo80 which may interact with the Pho4 protein.