PROTEIN PHOSPHATASE TYPE-1 INTERACTS WITH PROTEINS REQUIRED FOR MEIOSIS AND OTHER CELLULAR PROCESSES IN SACCHAROMYCES-CEREVISIAE

Protein phosphatase type 1 (PP1) is involved in diverse cellular proce sses, and its activity toward specific substrates is thought to be con trolled by different regulatory or targeting subunits. To identify reg ulatory subunits and substrates of the Saccharomyces cerevisiae PP1, e ncoded by GLC7, we used the two-hybrid system to detect interacting pr oteins. Among the many proteins identified were Gac1, a known glycogen regulatory subunit, and a protein with homology to Gac1. We also char acterized a new gene designated GIP1, for Glc7-interacting protein. We show that a Gip1 fusion protein coimmunoprecipitates with PP1 from ce ll extracts. Molecular and genetic analyses indicate that GIP1 is expr essed specifically during meiosis, affects transcription of late meiot ic genes, and is essential for sporulation. Thus, the Gip1 protein is a candidate for a meiosis-specific substrate or regulator of PP1. Fina lly, we recovered,two genes, RED1 and SCD5, with roles in meiosis and the vesicular secretory pathway, respectively. These results provide s trong evidence implicating PP1 function in meiosis. In addition, this study indicates that the two-hybrid system offers a promising approach to understanding the multiple roles and interactions of PP1 in cellul ar regulation.