The protein kinase homologue Ste20p is required to link the yeast pheromone response G-protein beta gamma subunits to downstream signalling components.

Abstract

In the yeast Saccharomyces cerevisiae the G-protein βγ 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 Gβγ to downstream components of the signalling pathway. Overproduction of the kinase suppresses the mating defect of dominant-negative Gβ mutations providing genetic evidence for an interaction with Gβ, and epistasis experiments show that this kinase functions after or at the same point as Gβγ, 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 Gβγ.