Fig. 1.

Cell-type regulation circuitry. The three yeast cell types and the regulatory proteins encoded by the MAT locus are depicted. These proteins, together with Mcm1, which is encoded elsewhere in the genome, govern expression of three sets of genes: a-specific genes, α-specific genes, and a1·α-repressed genes. See text for additional details. Also note that one of the a1·α2-repressed genes is MAT α1. This repression therefore precludes expression of α-specific genes in the a/α cell type. (Figure courtesy of D. Galgoczy and A. D. Johnson.)