title: The DNA of UV-irradiated normal and excision-deficient mammalian cells undergoes relaxation in an initial stage of DNA repair.
abstract: Using a radioimmunoassay specific for Pyr(6-4)Pyo photoproducts, we have demonstrated the removal of these lesions from denaturated DNA isolated from UV-irradiated Chinese hamster ovary cells at various times post irradiation. When assayed undenatured, these same DNA samples, which are initially 10-20 times less capable of binding antibody, show a substantial increase in binding capacity during the first few hours of repair. At 3 h post irradiation the difference between native and heat-denatured DNA samples is negligible, indicating that all of the residual lesions are contained in a single-stranded (relaxed) configuration. This relaxation also occurs in UV-hypersensitive cell lines, that are deficient in the ability to remove Pyr(6-4)Pyo photoproducts. Novobiocin, an inhibitor of topoisomerase II, prevents both the initial increase in binding and the subsequent excision of the antibody-binding sites.
mesh_terms: D000818:Animals; D002460:Cell Line; D006224:Cricetinae; D004247:DNA / Q000528:radiation effects*; D004260:DNA Repair / Q000187:drug effects; D004278:DNA, Superhelical; D009675:Novobiocin / Q000494:pharmacology; D009690:Nucleic Acid Conformation; D014466:Ultraviolet Rays
chemical_list: D004278:DNA, Superhelical; D009675:Novobiocin; D004247:DNA