A DNA-binding protein has been identified from extracts of the budding yeast Saccharomyces cerevisiae which binds to sites present in the promoter regions of a number of yeast genes transcribed by RNA polymerase II, including SIN3 (also known as SDI]), SWIS, CDC9, and TOP]. This protein also binds to a site present in the enhancer for the 35S rRNA gene, which is transcribed by RNA polymerase I, and appears to be identical to the previously described REB1 protein (B. E. Morrow, S. P. Johnson, and J. R. Warner, J. Biol. Chem. 264:9061-9068, 1989 Along with bypassing the SWI5 requirement, the sin3 mutation permits HO expression in daughters (27,33). Additionally, it was observed that a DNA-binding protein which recognizes a sequence in the HO promoter was deficient in sin3 extracts (27)