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The mating response pathway of the yeast Saccharomyces cerevisiae includes a heterotrimeric guanine nucleotide-binding protein (G protein) that activates a mitogenactivated protein (MAP) kinase cascade by an unknown mechanism. An amino-terminal fragment of the MAP kinase scaffold protein Ste5p that interfered with pheromoneinduced cell cycle arrest was identified. A haploid-specific interaction between the amino terminus of Ste5p and the G protein β subunit Ste4p was also detected in a two-hybrid assay, and the product of a signaling-defective allele of STE4 was defective in this interaction. In cells with a constitutively activated pheromone response pathway, epitopetagged Ste4p was coimmunoprecipitated with Ste5p. Thus, association of the G protein and the MAP kinase cassette via the scaffolding protein Ste5p may transmit the G protein signal., The pheromone response pathway of S. cerevisiae is a well-studied system of signal transduction (1, 2). Many genes that are required for haploid yeast cells to mate have been identified [...]

Reports on the identification of an amino-terminal fragment of the mitogen-activated protein (MAP) kinase scaffold protein Ste5p that interfered with pheromone-induced cell cycle arrest. Examination of the association of mutant versions of Ste4p with the Ste5p NH-terminal; Correlation between mutants defective in signaling.