CHARACTERIZATION OF A HUMAN DNA-DAMAGE BINDING-PROTEIN IMPLICATED IN XERODERMA-PIGMENTOSUM-E

A human DNA damage binding protein implicated in the DNA excision repa ir disorder xeroderma pigmentosum E was purified to near homogeneity f rom HeLa cells. The protein is abundant (approximately 10(5) copies/ce ll) and has a native molecular weight of 154,000-163,000 as estimated by gel filtration and glycerol gradient sedimentation. DNA damage bind ing activity copurified with polypeptides of 124 and 41 kDa. Based on the native molecular weight, cosedimentation of both polypeptides with DNA damage binding activity on glycerol gradients, and a molar ratio of approximately 1:1 for the two polypeptides, it appears that p124 an d p41 are subunits of a heterodimeric protein. Binding to damaged DNA was resistant to K+ concentrations approaching 1 M, but showed anion-s pecific sensitivity to Cl- concentrations above 0.5 M, suggesting that the majority of the binding energy is contributed by nonionic interac tions. In contrast to previous reports, the DNA damage binding protein was shown to recognize cyclobutane pyrimidine dimers in addition to a nonphotoreactivable lesion(s), most likely the pyrimidine-pyrimidone (6-4) photoproduct.