Purification of intercalator-released p67, a polypeptide that interacts specifically with the c-fos serum response element.

Incubation of intact nuclei in buffers containing the DNA intercalating drug chloroquine leads to release of proteins that interact with DNA. We demonstrate here that a protein which binds to a motif within the human c-fos promoter, identified as the serum response element (SRE), is quantitatively released from HeLa nuclei, whereas nuclear factor 1 (NF 1) is not. Purification of the SRE binding protein by affinity chromatography to greater than 95% homogeneity allowed us to identify it as a polypeptide of approximately 67,000 daltons. The DNA contacts made by p67, as identified by methylation interference experiments, are indistinguishable from those of the serum response factor described previously.