Negative regulators of the PHO system of Saccharomyces cerevisiae: characterization of PHO80 and PHO85.

Both PHO80 and PHO85 genes are required to establish the repressed state of the PHO system of Saccharomyces cerevisiae. S1 nuclease protection analysis of the PHO85 transcript revealed that the PHO85 gene contains an intron at the 6th codon of the gene. Each of the fusion proteins, LacZ-Pho80 and LacZ-Pho85, was produced into Escherichia coli and used as an antigen to raise antibodies in a rabbit. Using the affinity-purified antibodies in Western blotting experiments, the PHO85 protein was detected as a 36 kDa and the PHO80 protein as a 34 kDa protein. The PHO80 protein was detected only in extracts prepared from an overproducing strain. The immunoprecipitate containing the PHO85 protein showed protein kinase activity suggesting that PHO85 is a protein kinase gene, which is consistent with the observation that the deduced amino acid sequence of the PHO85 protein resembles that of some protein kinases. The PHO80 protein was found to be phosphorylated in the presence of PHO85 protein.