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

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Abstract
In the yeast Saccharomyces cerevisiae the G‐protein beta gamma 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 beta gamma 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 beta gamma, 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 beta gamma.