a1 protein alters the DNA binding specificity of alpha 2 repressor.
The alpha 2 protein of S. cerevisiae, the product of the MAT alpha 2 gene, represses a set of cell-type-specific genes (the a-specific genes) by binding to an operator sequence upstream of each gene. We demonstrate that a second yeast regulatory protein, a1, the product of the MATa1 gene, can alter the binding specificity of alpha 2 so that it no longer recognizes the a-specific gene operator, but instead acquires the ability to recognize a different operator sequence found upstream of haploid-specific genes. Thus, under the influence of a1, alpha 2 can repress haploid-specific genes. An alpha cell expresses alpha 2 but not a1, so that alpha 2 turns off only the a-specific genes. An a/alpha cell makes both a1 and alpha 2, in a ratio that ensures that alpha 2 is distributed between two distinct binding modes: the alpha 2 binding mode and the a1-alpha 2 binding mode. Thus in an a/alpha cell, alpha 2 represses two distinct classes of genes.
D002872:Chromosome Deletion; D005796:Genes; D005800:Genes, Fungal; D005809:Genes, Regulator; D000072235:Mating Factor; D009154:Mutation; D010455:Peptides / Q000502:physiology*; D010675:Pheromones / Q000502:physiology*; D012097:Repressor Proteins / Q000378:metabolism*; D012441:Saccharomyces cerevisiae / Q000235:genetics*; D014157:Transcription Factors / Q000378:metabolism*; D001616:beta-Galactosidase / Q000235:genetics
D010455:Peptides; D010675:Pheromones; D012097:Repressor Proteins; D014157:Transcription Factors; D000072235:Mating Factor; D001616:beta-Galactosidase