Both activation and repression of a-mating-type-specific genes in yeast require transcription factor Mcm1.

Mcm1 is a yeast transcription factor with homologs throughout the metazoa. MCM1 was first identified as a gene involved in maintenance of artificial minichromosomes in yeast. More recently Mcm1 has been shown to serve as a transcriptional regulator of mating-type-specific genes. Biochemical data suggest that Mcm1 coactivates alpha-specific genes and corepresses a-specific genes by binding to a 10-base-pair dyad symmetry element in their upstream regions. We reported previously that an mcm1 point mutation reduced activation of alpha-specific genes but had little effect on the expression of a-specific genes. We now show that another mcm1 allele, which depletes the Mcm1 protein, affects both activation and repression of a-specific genes. The mutant strain remains capable of high levels of pheromone induction of a-specific genes, although with retarded kinetics. Mcm1 joins an increasing number of transcription factors involved in both positive and negative regulation of gene expression.