Regulation by the yeast mating-type locus of STE12, a gene required for cell-type-specific expression.

The STE12 gene of the yeast Saccharomyces cerevisiae is necessary for RNA synthesis from two sets of cell-type-specific genes. We isolated a recombinant plasmid that carries the STE12 gene by complementation of the mating defect of ste12 cells. The DNA of the cloned gene was used to disrupt the chromosomal STE12 gene and to identify the STE12 transcript. We show that the STE12 transcript level is repressed 5- to 10-fold in a/alpha cells. The STE12 product thus acts to promote diploidy by activating expression of the two sets of genes necessary for mating, and then its synthesis is repressed by products unique to the diploid cell type.