THE REG2 GENE OF SACCHAROMYCES-CEREVISIAE ENCODES A TYPE-1 PROTEIN PHOSPHATASE-BINDING PROTEIN THAT FUNCTIONS WITH REG1P AND THE SNF1 PROTEIN-KINASE TO REGULATE GROWTH

The GLC7 gene of Saccharomyces cerevisiae encodes the catalytic subuni t of type 1 protein phosphatase (PP1) and is essential for cell growth , We have isolated a previously uncharacterized gene, REG2, on the bas is of its ability to interact with Glc7p in the two-hybrid system, Reg 2p interacts with Glc7p in vivo, and epitope-tagged derivatives of Reg 2p and Glc7p coimmunoprecipitate from cell extracts. The predicted pro tein product of the REG2 gene is similar to Reg1p, a protein believed to direct PP1 activity in the glucose repression pathway, Mutants with a deletion of reg1 display a mild slow-growth defect, while reg2 muta nts exhibit a wild-type phenotype, However, mutants with deletions of both reg1 and reg2 exhibit a severe growth defect, Overexpression of R FG2 complements the slow-growth defect of a reg1 mutant but does not c omplement defects in glycogen accumulation or glucose repression, two traits also associated with a reg1 deletion. These results indicate th at REG1 has a unique role in the glucose repression pathway but acts t ogether with REG2 to regulate some as yet uncharacterized function imp ortant for growth, The growth defect of a reg1 reg2 double mutant is a lleviated by a loss-of-function mutation in the SNF1-encoded protein k inase. The snf1 mutation also suppresses the glucose repression defect s of reg1. Together, our data are consistent with a model in which Reg 1p and Reg2p control the activity of PP1 toward substrates that are ph osphorylated by the Snf1p kinase.