Postreplication repair of DNA in human fibroblasts after UV irradiation or treatment with metabolites of benzo(a)pyrene

We have examined the ability of normal fibroblasts and of excision-deficient xeroderma pigmentosum (XP) and XP variant fibroblasts to perform postreplication DNA repair after increasing doses of either ultraviolet (UV) irradiation or mutagenic benzo(a)pyrene derivatives. XP cells defective in the excision of both UV-induced pyrimidine dimers and guanine adducts induced by treatment with the 7,8-diol-9,10-epoxides of benzo(a)pyrene were partially defective in their ability to synthesize high molecular weight DNA after the induction of both classes of DNA lesions. This defect was more marked in XP variant cells, despite their ability to remove by excision repair both pyrimidine dimers and the diol epoxide-induced lesions to the same degree as observed in normal cells. The benzo(a)pyrene 9,10-oxide had no effect in any of the 3 cell lines. The response of the excision and postreplication DNA repair mechanisms operating in human fibroblasts treated with benzo(a)pyrene 7,8-diol-9,10-epoxides, therefore, appears to resemble closely that seen after the induction of pyrimidine dimers by UV irradiation.