Function of the ste signal transduction pathway for mating pheromones sustains MAT alpha 1 transcription in Saccharomyces cerevisiae.

Sterile mutants of Saccharomyces cerevisiae were isolated from alpha * cells having the a/alpha aar1-6 genotype (exhibiting alpha mating ability and weak a mating ability as a result of a defect in a1-alpha 2 repression). Among these sterile mutants, we found two ste5 mutants together with putative ste7, ste11, and ste12 mutants of the signal transduction pathway of mating pheromones. The amino acid sequence of the Ste5p protein predicted from the nucleotide sequence of a cloned STE5 DNA has a domain rich in acidic amino acids close to its C terminus, a cysteine-rich sequence, resembling part of a zinc finger structure, in its N-terminal half, and a possible target site of cyclic AMP-dependent protein kinase at its C terminus. Northern (RNA) blot analysis revealed that STE5 transcription is under a1-alpha 2-Aar1p repression. The MAT alpha 1 cistron has a single copy of the pheromone response element in its 5' upstream region, and its basal level of transcription was reduced in these ste mutant cells. However, expression of the MAT alpha 1 cistron was not enhanced appreciably by pheromone signals. One of the ste5 mutant alleles conferred a sterile phenotype to a/alpha aar1-6 cells but a mating ability to MATa cells.