Functional domains of the yeast transcription/replication factor MCM1

MCM1 is an essential yeast DNA-binding protein that affects both minichromosome maintenance, in a manner suggesting that it has DNA replication initiation function, and gene expression. It activates α-specific genes together with MATα1, and represses a-specific genes together with MATα2. Alone, MCM1 can activate transcription. To determine whether different domains of the protein mediate these diverse functions, we constructed and analyzed several mcm1 mutants. The gene expression and minichromosome maintenance phenotypes of these mutants suggest that the role of MCM1 in DNA replication initiation may not involve transcriptional activation. However, both transcription and replication activities require only the 80-amino-acid fragment of MCM1 homologous to the DNA-binding domain of the serum response factor (SRF). This small fragment is also sufficient for cell viability and repression of a-specific genes. A polyacidic amino acid stretch immediately adjacent to the SRF homologous domain of MCM1 was found to be important for activation of α-specific genes in α cells. Mutants lacking the acidic stretch confer higher expression from an α-specific UAS in a cells in addition to lower expression in α cells, suggesting that negative regulation at this site occurs in a cells, in addition to the well-documented positive regulation in α cells