Differential XPC ubiquitylation in chromatin.
(A) UV-dependent ubiquitylation of XPC protein visualized by an immunoblot of HeLa whole-cell lysates 15 min after UV irradiation (30 J/m2). Ubn, ubiquitylated forms of XPC. (B) The chromatin of HeLa cells was dissected by MNase digestion (4 U/µl) at different times after UV exposure to compare the ubiquitylation of XPC bound to the core particle fraction (“I. cores”) or internucleosomal DNA (“S. inter.”). (C) Quantitative comparison of ubiquitylated XPC relative to total XPC associated with either solubilizable (4 U/µl) internucleosomal sites (“S. inter.”) or MNase-resistant core particles (“I. cores”) at the indicated times after UV irradiation (mean values of two independent determinations). (D) Representative blot illustrating the DDB2 degradation and long-term binding of XPC to the insoluble core particle fraction (“I. cores”) after UV exposure. (E) Quantification of the time-dependent XPC distribution in the chromatin of UV-exposed HeLa cells. XPC amounts in the core particle fraction (“I. cores”) and at internucleosomal sites (“S. inter.”) were calculated from Western blots followed by corrections for the different loading as indicated in panel D (mean values of three independent determinations).