Characterization of the CP complex, an abundant dimer of Cdc68 and Pob3 proteins that regulates yeast transcriptional activation and chromatin repression

The Cdc68 protein of the yeast Saccharomyces cerevisiae is an essential nuclear protein that has been shown to be necessary for the trans-activation of many genes as well as for the maintenance of chromatin-mediated repression in the absence of trans-activation. These activities implicate the Cdc68 protein in the regulation of chromatin structure and/or function. Here we report that Cdc68 is found in association with another essential nuclear protein, Pob3, in what we term the CP complex. This dimer of Cdc68 with Pob3 is stable to partial purification, so that the functions of gene activation and repression that are assigned to Cdc68 are likely to be properties of the CP complex. The CP complex is highly abundant, suggesting that it may be widespread throughout chromatin.