Transcription and regulatory signals at the mating type locus in yeast

The mating type locus with two alleles (MATa and MAT alpha) determines cell type in yeast by activating and repressing sets of cell-type-specific genes. The two genes at MAT alpha, alpha 1 and alpha 2, are transcribed divergently from a central promoter region. Deletions in this intergenic region have been used to map DNA sequences involved in the transcription and regulation of the MAT alpha genes. A single promoter region, essential for transcription of both alpha 1 and alpha 2, is found in the region between alpha 1 and alpha 2. Deletions removing the alpha 1 or alpha 2 TATA box are still transcribed but the transcripts fail to initiate properly. A separate regulatory region is also found between alpha 1 and alpha 2. Deletions of this region lead to the constitutive expression of these genes. These regulatory mutants synthesize alpha 1 mRNA in diploids, but this is not sufficient to activate the alpha-specific genes.