Identification and Characterization of a Mutation Affecting the Division Arrest Signaling of the Pheromone Response Pathway in Saccharomyces Cerevisiae

Mating pheromones, a- and alpha-factors, arrest the division of cells of opposite mating types, alpha and a cells, respectively. I have isolated a sterile mutant of Saccharomyces cerevisiae that is defective in division arrest in response to alpha-factor but not defective in morphological changes and agglutinin induction. The mutation was designated dac2 for division arrest control by mating pheromones. The dac2 mutation was closely linked to gal1 and was different from the previously identified cell type nonspecific sterile mutations (ste4, ste5, ste7, ste11, ste12, ste18 and dac1). Although dac2 cells had no phenotype in the absence of pheromones, they showed morphological alterations and divided continuously in the presence of pheromones. As a result, dac2 cells had a mating defect. The dac2 mutation could suppress the lethality caused by the disruption of the GPA1 gene (previously shown to encode a protein with similarity to the alpha subunit of mammalian G proteins). In addition, dac2 cells formed prezygotes with wild-type cells of opposite mating types, although they could not undergo cell fusion. These results suggest that the DAC2 product may control the signal for G-protein-mediated cell-cycle arrest and indicate that the synchronization of haploid yeast cell cycles by mating pheromones is essential for cell fusion during conjugation.