A repressor (MAT alpha 2 Product) and its operator control expression of a set of cell type specific genes in yeast

The product of the yeast MAT alpha 2 gene, alpha 2 protein, negatively regulates expression of a class of yeast cell type specific genes, the a-specific genes. In this paper we show that alpha 2 is a sequence-specific DNA binding protein. It recognizes a 32 base pair DNA sequence (operator) located upstream of an a-specific gene, STE6. A strongly homologous sequence is present upstream of each of the other four known a-specific genes. A synthetic STE6 operator, when placed in a test promoter (CYC1), brings the promoter under negative control by alpha 2 in vivo. This operator brings about repression when it is placed between the CYC1 upstream activation sequence (UAS) and the transcription start and when it is placed upstream of the UAS, outside the promoter. Thus, the operator need not overlap with essential promoter sequences to permit repression by alpha 2.