Purification of a novel 55 kDa HeLa cell nuclear DNA-binding protein.

A novel 55 kDa DNA-binding protein (p55) was purified from HeLa cell nuclear extracts to apparent homogeneity by conventional chromatography coupled with DNA-affinity chromatography. The DNA-binding activity of p55, followed by band mobility shift and Southwestern assays, was enriched 800-fold. This relatively abundant protein was shown to bind nonspecifically to DNA. When added to nuclear extracts, p55 enhanced 2-fold the in vitro transcription of CAT reporter gene driven by the SV40 promoter. The sequence of the N-terminal 20 amino acid residues of purified p55 was determined as APSTPLLTV(P)G(S)EGLYMVNG, homologies could be found when compared to protein sequences available in all databanks.