The yeast STE12 product is required for expression of two sets of cell-type specific genes.

Yeast alpha and a cells transcribe distinct sets of genes involved in mating behavior, alpha-specific genes and a-specific genes, respectively. The alpha 1 product of the alpha mating type locus (MAT alpha) has been the only known activator of either set of genes; it is required for synthesis of RNA from the alpha-specific genes, one of which is the major alpha-factor gene. By screening for mutants that are no longer able to express this gene, we have identified the STE12 gene product as another positive regulator of the alpha-factor gene. alpha ste12 cells are also defective in RNA production from the other known alpha-specific genes. Moreover, a ste12 cells fail to produce wild-type levels of RNA from the a-specific genes. The STE12 gene product is therefore an activator of two sets of genes involved in yeast cell type specialization.