INDUCTION AND REPAIR OF DNA-DAMAGE IN UV-IRRADIATED HUMAN-LYMPHOCYTES- SPECTRAL DIFFERENCES AND REPAIR KINETICS

The alkaline elution assay has been employed to study the induction an d repair kinetics of DNA damage in human lymphocytes after irradiation with biologically relevant doses of UVB (297 and 302 nm) or UVA (365 nm) radiation. At 365 nm, when the predominant lesions are single-stra nd breaks, the rate of lesion induction was 1.5 X 10(-3) per 10(8) Da per kJ m(-2). The number of breaks decayed with a half-life of about 5 0 min after a dose of 20 kJ m(-2). In the UVB region, cyclobutyl pyrim idine dimers and 6-4 photoproducts are formed, both of which are repai rable via the nucleotide excision repair pathway. By using repair inhi bitors, the rate of induction of such lesions at 297 and 302 nm was fo und to be 0.07 per 10(8) Da per J m(-2). Lesions were removed with a h alf-life of about 100 min. Mathematical modelling of the excision repa ir process revealed a time-dependent polymerization-ligation rate: aft er an initial lag phase the polymerization-ligation rate increased, re aching 50% of its maximum rate at 80-100 min after the start of repair incubation. This course of development might be due to a damage-assoc iated regulation of DNA precursors synthesis.