STE16, a New Gene Required for Pheromone Production by a Cells of Saccharomyces cerevisiae

Genes required for mating by a and α cells of Saccharomyces cerevisiae (STE, "sterile," genes) encode products such as peptide pheromones, pheromone receptors, and proteins responsible for pheromone processing. a-specific STE genes are those required for mating by a cells but not by α cells. To identify new a-specific STE genes, we have employed a novel strategy that enabled us to determine if a ste mutant defective in mating as a is also defective in mating as α without the need to do crosses. This technique involved a strain (K12-14b) of genotype mat  a  1 HML? HMR? sir3ts, which mates as a at 25° and as α at 34°. We screened over 40,000 mutagenized colonies derived from K12-14b and obtained 28 a-specific ste mutants. These strains contained mutations in three known a-specific genes- STE2, STE6 and STE14-and in a new gene, STE16. ste16 mutants are defective in the production of the pheromone, a-factor, and exhibit slow growth. Based on the distribution of a-specific ste mutants described here, we infer that we have identified most if not all nonessential genes that can give rise to a-specific mating defects.