The yeast Mcm1 protein is a founding member of the MADS-box family of transcription factors that is involved in the regulation of diverse sets of genes through interactions with distinct cofactor proteins. Mcm1 interacts with the Matα1 protein to activate the expression of the α-cell type-specific genes. To understand the requirement of the cofactor α1 for Mcm1-α1-dependent transcriptional activation we analyzed the recruitment of Mcm1 to the promoters of α-specific genes in vivo and found that Mcm1 is able to bind to the promoters of α-specific genes in the absence of α1. This suggests the function of α1 is more complex than simply recruiting Mcm1. Several MADS-box transcription factors, including Mcm1, induce DNA bending and there is evidence the proper bend may be required for transcriptional activation. We analyzed Mcm1-dependent bending of a Mcm1-α1 binding site in the presence and absence of α1 and found that Mcm1 alone shows a reduced DNA-bend at this site compared with other Mcm1 binding sites. However, the addition of α1 markedly increases the DNA-bend and we present evidence this bend is required for full transcriptional activation. These results support a model in which proper DNA-bending by the Mcm1-α1 complex is required for transcriptional activation.
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