PPQ, A NOVEL PROTEIN PHOSPHATASE CONTAINING A SER PLUS ASN-RICH AMINO-TERMINAL DOMAIN, IS INVOLVED IN THE REGULATION OF PROTEIN-SYNTHESIS

The sequence of a Saccharomyces cerevisiae cDNA encoding a novel 61-kD a protein serine/threonine phosphatase, termed PPQ1, is presented. The protein consists of two distinct domains: the carboxy-terminal phosph atase domain is approximately 60% identical to either PP1 or the carbo xy-terminal domains of PPZ1 and PPZ2, while the amino-terminal region is rich in serine and asparagine. Deletion of the gene encoding PPQ1 r educes cell growth on several carbon sources, and lowers cell density in the stationary phase. Cells in which PPQ1 gene has been deleted sho w altered morphology from wild-type cells in the stationary phase in t he absence of an essential amino acid and a reduced rate of protein sy nthesis in the exponential phase. They are hypersensitive to the prote in synthesis inhibitors, cycloheximide and G418, implicating PPQ1 in t he regulation of translation.