MOLECULAR ANALYSIS OF THE PHO81 GENE OF SACCHAROMYCES-CEREVISIAE

The PHO81 gene product is a positive regulatory tactor required tor th e synthesis of the phosphate repressible acid phosphatase (encoded by the PHO5 gene) in Saccharomyces cerevisiae. Genetic analysis has sugge sted that PHO81 may be the signal acceptor molecule; however, the bioc hemical function of the PHO81 gene product is not known. We have clone d the PHO81 gene and sequenced the promoter. A PHO81-LacZ fusion was s hown to be a valid reporter since its expression is regulated by the l evel of inorganic phosphate and is controlled by the same regulatory t actors that regulate PHO5 expression. To elucidate the mechanism by wh ich PHO81 functions, we have isolated and cloned dominant mutations in the PHO81 gene which confer constitutive synthesis of acid phosphatas e. We have demonstrated that overexpression of the negative regulatory tactor, PHO80, but not the negative regulatory tactor PHO85, partiall y blocks the constitutive acid phosphatase synthesis in a strain conta ining a dominant constitutive allele of PHO81. This suggests that PHO8 1 may function by interacting with PHO80 or that these molecules compe te tor the same target.