Phosphorylation of Gβ is crucial for efficient chemotropism in yeast

Mating yeast cells interpret complex pheromone gradients and polarize their growth in the direction of the closest partner. Chemotropic growth depends on both the pheromone receptor and its associated G-protein. Upon activation by the receptor, Ga dissociates from G beta gamma and Gb is subsequently phosphorylated. Free G beta gamma signals to the nucleus via a MAPK cascade and recruits Far1-Cdc24 to the incipient growth site. It is not clear how the cell establishes and stabilizes the axis of polarity, but this process is thought to require local signal amplification via the G beta gamma-Far1-Cdc24 chemotropic complex, as well as communication between this complex and the activated receptor. Here we show that a mutant form of G beta that cannot be phosphorylated confers defects in directional sensing and chemotropic growth. Our data suggest that phosphorylation of G beta plays a role in localized signal amplification and in the dynamic communication between the receptor and the chemotropic complex, which underlie growth site selection and maintenance.