The C-terminal domain of SIN1 in yeast interacts with a protein that binds the URS1 region of the yeast HO gene

A protein or protein complex has previously been identified in Saccharomyces cerevisiae which both binds a short DNA sequence in URS1 of HO and interacts with SIN1. SIN1, which has some sequence similarity to mammalian HMG1, is an abundant chromatin protein in yeast and is thought to participate in the transcriptional repression of a specific family of genes. SIN1 binds DNA weakly, though it has no DNA binding specificity. Here we address the nature of the interaction between SIN1 and the specific DNA binding protein(s) to HO DNA. We show that the isolated C-terminal region of SIN1 can interact in vitro with the DNA binding protein, causing a supershift in a gel mobility shift assay. Interestingly, inclusion of the region in SIN1 which contains two acidic sequences, precludes the binding of recombinant protein to the DNA/protein complex.