The yeast transcription activator PRTF, a homolog of the mammalian serum response factor, is encoded by the MCM1 gene.

Two proteins, alpha 1 and pheromone/receptor transcription factor (PRTF), bind cooperatively to the upstream activation sequences (UAS) of yeast alpha-specific genes and thereby activate their transcription. In these protein-DNA complexes, the PRTF moiety interacts with a degenerate dyad symmetric sequence, the P box. PRTF contributes also to the regulation of a second set of cell-type-specific genes, the a-specific genes. We used two in vitro assays to show that PRTF is encoded, at least in part, by the MCM1 gene. In one assay, truncated MCM1 proteins encoded by deletion derivatives of the MCM1 gene formed protein-DNA complexes of novel mobility, demonstrated that MCM1 can bind to the P-box-containing DNA. Second, antibodies raised to a synthetic MCM1 polypeptide retard the migration of PRTF-DNA complexes in gel mobility shift assays. This result indicates that PRTF, defined as an activity that binds cooperatively with alpha 1 to alpha-specific UAS elements, shares an epitope with MCM1. In addition, we show that MCM1 deletions that remove the carboxy-terminal 129 codons of 286 total codons encode truncated MCM1 molecules that are competent to activate transcription in vivo, indicating that the carboxy-terminal residues are not required for this process.