MSG5, A NOVEL PROTEIN PHOSPHATASE PROMOTES ADAPTATION TO PHEROMONE RESPONSE IN SACCHAROMYCES-CEREVISIAE

Pheromone-stimulated yeast cells and haploid gpa1 deletion mutants arr est their cell cycle in G(1). Overexpression of a novel gene called MS G5 suppresses this inhibition of cell division. Loss of MSG5 function leads to a diminished adaptive response to pheromone. Genetic analysis indicates that MSG5 acts at a stage where the protein kinases STE7 an d FUS3 function to transmit the pheromone-induced signal. Since loss o f MSG5 function causes an increase in FUS3 enzyme activity but not STE 7 activity, we propose that MSG5 impinges on the pathway at FUS3. Sequ ence analysis suggests that MSG5 encodes a protein tyrosine phosphatas e. This is supported by the finding that recombinant MSG5 has phosphat ase activity in vitro and is able to inactivate autophosphorylated FUS 3. Thus MSG5 might stimulate recovery from pheromone by regulating the phosphorylation state of FUS3.