Glc7p protein phosphatase inhibits expression of glutamine-fructose-6-phosphate transaminase from GFA1

Inhibitor-1 (I-1) is a specific inhibitor of protein phosphatase-l (PP1). W e assayed the ability of I-1 to inhibit Saccharomyces cerevisiae PP1, Glc7p , in vivo. Glc7p hire other PP1 catalytic subunits associates with a variet y of noncatalytic subunits, and Glc7p holoenzymes perform distinct physiolo gical roles. Our results show that I-1 inhibits Glc7p holoenzymes that regu late transcription and mitosis, but holoenzymes responsible for meiosis and glycogen metabolism were unaffected. Additionally, we exploited a genetic screen for mutants that were dependent on I-1 to grow. This scheme can iden tify processes that are negatively regulated by Glc7p-catalyzed dephosphory lation. In this paper I-I-dependent gfa1 mutations were analyzed in detail. GFA1 encodes glutamine-fructose-6-phosphate transaminase. One or more phos phorylated proteins activate GFA1 transcription because the pheromone respo nse and Pkc1p/mitogen-activated protein kinase pathways positively regulate GFA1 transcription Our findings show that an I-1-sensitive Glc7p holoenzym e reduces GFA1 transcription. Therefore, GFA1 is a member of a growing list of genes that are negatively regulated by Glc7p dephosphorylation.