REMOVAL OF UV-INDUCED DNA LESIONS IN MOUSE EPIDERMIS SOON AFTER IRRADIATION

Induction and removal of cyclobutane thymine dimers and (6-4)photoprod ucts were studied in epidermal DNA isolated from UV-exposed hairless m ice. For the detection of DNA damage, lesion-specific monoclonal antib odies were used in an immunoslotblot assay. Following the exposure of mice to 3.0 kJ m(-2) UV-B, substantial removal of both thymine dimers (66%) and (6-4)photoproducts (77'%) was observed at 24 h after irradia tion. No removal, however, was detected at 4 h after irradiation. In c ontrast, immunofluorescence data obtained previously showed a rapid in itial dimer removal after irradiation with 1.0 kJ m(-2) UV-B (A.A. Vin k, R.J.W. Berg, F.R. De Gruijl, L. Roza and R.A. Baan, Carcinogenesis, 12 (1991) 861-864.) Reinvestigation of the removal of dimers and (6-4 )photoproducts shortly after three different UV doses showed a rapid d ecrease of both lesions at 2 h after irradiation with 1.0 W m(-2). The results obtained after irradiations with 2.0 and 3.0 kJ m(-2) UV-B su ggest a saturation of repair already at 2.0 kJ m(-2). Cyclobutane dime rs were found to be removed at a lower rate than (6-4)photoproducts.