far4, far5, and far6 define three genes required for efficient activation of MAPKs Fus3 and Kss1 and accumulation of glycogen

In Saccharomyces cerevisiae, mating pheromones induce G1 arrest through the activation of two MAP kinases. Fus3 and Kss1. Here we report the isolation of three mutants, far4, far5.. and far6, that have the novel phenotype of regulating both the activity of Fus3 and Kss1 and the accumulation of glycogen. Afar4 mutation constitutively activates Fus3 and Kss1. reduces glycogen, and blocks G1 arrest in the presence of alpha factor. In contrast, far5 and far6 mutations increase glycogen and reduce activation of Fus3 and Kss1 by pheromone. far4, far5, and far6 are recessive and not allelic to FAR1, FAR3, or 14 genes known to regulate the pheromone response. Non-allelic non-complementation occurs between far6 and both far4 and far5, suggesting that FAR6 functionally interacts with FAR4 and FAR5. Additional observations suggest that FAR4 has functional overlap with FAR3, which we also find to regulate glycogen accumulation. Our results suggest that the activation of the mating MAPK cascade and subsequent G1 arrest is influenced by a signal transduction pathway that regulates glycogen. In support of this possibility, we find that Fus3 is activated to a greater extent in a "wimp" strain with defective protein kinase A. Finally, BIM1 and BIK1 have been identified as CEN Suppressors of far5, suggesting that the microtubule apparatus may regulate the ability of the pheromone response pathway to promote G1 arrest.