COMPLEX REPAIR KINETICS OF DNA STRAND BREAKS INDUCED BY GAMMA-RAYS ORUV-RADIATION IN EHRLICH ASCITES TUMOR-CELLS

Fluorometric analysis of DNA unwinding (FADU)-a sensitive technique fo r the detection of strand breaks in DNA-has been modified and used for the detailed investigation of repair kinetics of DNA-strand breaks ar ising under different condtions in Ehrlick ascites tumour (EAT) cells irradiated by gamma-rays or ultraviolet (UV) radiation. The repair kin etics of DNA-strand breaks induced in EAT cells by gamma-radiation was measured at radiation doses of 8, 20 and 50 Gy. We found complex repa ir curves in all cases, probably reflecting the combined processes of break rejoining and break generation during repair. In order to affect the above-mentioned processes, we have used different conditions of r epair and different types of radiation. Lowering of the temperature of incubation and treating the cells by 5-fluoro-2'deoxyuridine (FUdR) l ead to complex changes of the repair curve with a reduced ''wave'' pat tern. In order to change the type of damage to DNA, we used UV radiati on (254 nm, 10 and 20 J/M(2)). Detailed studies of the repair kinetics showed that the repair curve for 10 J/m(2) had a second maximum withi n 70 min after irradiation.