Identification and characterization of FAR3, a gene required for pheromone-mediated G1 arrest in Saccharomyces cerevisiae.

In haploid Saccharomyces cerevisiae cells, mating pheromones activate a signal transduction pathway that leads to cell cycle arrest in the G1 phase and to transcription induction of genes that promote conjugation. To identify genes that link the signal transduction pathway and the cell cycle machinery, we developed a selection strategy to isolate yeast mutants specifically defective for G1 arrest. Several of these mutants identified previously known genes, including CLN3, FUS3, and FAR1. In addition, a new gene, FAR3, was identified and characterized. FAR3 encodes a novel protein of 204 amino acid residues that is dispensable for viability. Northern blot experiments indicated that FAR3 expression is constitutive with respect to cell type, pheromone treatment, and cell cycle position. As a first step toward elucidating the mechanism by which Far3 promotes pheromone-mediated G1 arrest, we performed genetic and molecular experiments to test the possibility that Far3 participates in one of the heretofore characterized mechanisms, namely Fus3/Far1-mediated inhibition of Cdc28-Cln kinase activity, G1 cyclin gene repression, and G1 cyclin protein turnover. Our data indicate that Far3 effects G1 arrest by a mechanism distinct from those previously known.