THE PROTEIN-KINASE HOMOLOG STE20P IS REQUIRED TO LINK THE YEAST PHEROMONE RESPONSE G-PROTEIN BETA-GAMMA SUBUNITS TO DOWNSTREAM SIGNALING COMPONENTS

In the yeast Saccharomyces cerevisiae the G-protein betagamma subunits have been shown to trigger downstream events of the pheromone response pathway. We have identified a new gene, designated STE20, which encodes a protein kinase homologue with sequence similarity to protein kinase C, which is required to transmit the pheromone signal from G(betagamma) to downstream components of the signalling pathway. Overproduction of the kinase suppresses the mating defect of dominant-negative G(beta) mutations providing genetic evidence for an interaction with G(beta), and epistasis experiments show that this kinase functions after or at the same point as G(betagamma), but before any of the other currently identified components of the signalling pathway. This points to a potentially new mechanism of G-protein mediated signal transduction, the activation of a protein kinase through G(betagamma).