Far1

Far1 is a gene in the budding yeast Saccharomyces cerevisiae encoding a cytoplasmic protein that mediates the cellular response to mating pheromone. The protein is a key regulator linking the alpha-factor pheromone signal to two outcomes: G1 cell cycle arrest and pheromone-directed morphogenesis, or shmoo formation, enabling cells to mate.

Mechanism and function. Upon exposure to alpha-factor, the GPCR Ste2 activates the G protein Gpa1. Far1 binds to Gpa1-GTP and functions as a scaffold that recruits the Cdc24–Cdc42 module to the plasma membrane. This localization promotes localized activation of Cdc42 and polarized growth toward the pheromone source. In parallel, Far1 interacts with the Cln1/2–Cdc28 cyclin-dependent kinase complex and inhibits its activity, enforcing G1 cell cycle arrest during mating.

Regulation and interactions. Far1 activity is regulated by pheromone signaling and post-translational modifications, which influence its localization and binding partners. Through its dual roles, Far1 coordinates the spatial cues for polarity with cell cycle control, helping the cell commit to mating rather than division.

Genetic and phenotypic effects. Deletion of FAR1 impairs pheromone-induced G1 arrest and reduces efficiency of shmoo formation, reflecting defects in both cell cycle control and polarized growth. Overexpression can amplify pheromone responses. FAR1 genetically interacts with CDC24, CLN1, and components of the pheromone signaling pathway, illustrating its central role in integrating signaling and morphogenesis.

Overview. Far1 is a model example of how a single regulator can mediate both cell cycle arrest and directed morphogenesis in response to environmental cues, highlighting the coordination between signaling, polarity, and division in yeast.