Order of Action of Components in the Yeast Pheromone Response Pathway Revealed with a Dominant Allele of the STE11 Kinase and the Multiple Phosphorylation of the STE7 Kinase

The signal transduction pathway that mediates the response of haploid yeast cells to peptide mating pheromones involves several components including the protein kinases STE7 and STE11. We have isolated and characterized a dominant allele of the STE11 gene and have demonstrated that expression of an amino-terminally truncated form of STE11 protein causes constitutive activation of the mating pathway. Expression of this dominant STE11 allele also restored mating ability to certain sterile strains. In conjunction with the results of others, our epistasis results establish the following order of action of pathway components: STE2, GPA1(SCG1), STE4, STE5, STE11, STE7, STE12. Transduction of the signal from STE11 to STE7 may involve phosphorylation because STE7 displays several phosphorylation forms, and STE7 is multiply phosphorylated in response to either pheromone or coexpression of dominant STE11 protein. Further signal propagation appears to require STE7 protein kinase activity, because a catalytically impaired STE7 mutant is defective in the mating response.