CHARACTERIZATION AND EVALUATION BY P-32 POSTLABELING OF PSORALEN TYPEDNA-ADDUCTS IN HELA-CELLS

Samples of DNA irradiated at 405 and/or 365 mm in the presence of 8-me thoxypsoralen (8-MOP) were analysed via a modified postlabelling assay using three hydrolysis enzymes other than those employed previously. These enzymes (deoxyribonucleaseI, venom phosphodiesterase and alkalin e phosphatase) liberated 3'-adducted dinucleotide monophosphate instea d of the 5'-modified dinucleotide monophosphate normally obtained. The first separation chromatography (D1) of samples irradiated in the pre sence of 8-MOP showed a single spot above the origin, and the next sep aration (D2) resolved this spot into two components (spots I and D). D ouble irradiation experiments in which samples of DNA were first irrad iated at 405 mm before being irradiated at 365 nm showed that spot in could be transformed into spot I. The use of 6,4,4'-trimethylangelicin , which induced only photomonoadducts under UVA irradiation, gave only spot II. These two results indicated that spots I and II were respect ively due to interstrand cross-links and monoadducts. Dose-effect expe riments showed that spots I and II were dose dependent, and low-dose i rradiations permitted us to measure one interstrand cross-link and two monoadducts per 10(8) base pairs.