Impaired repair of UVC-induced DNA damage in L5178Y-R cells: sedimentation studies with the use of 5'-bromodeoxyuridine photolysis

Relative to their L5178Y-S counterparts, L5178Y-R cells have an impaired capacity to form patches in DNA after exposure to UVC radiation. The photolysis of 5'-bromodeoxyuridine (BrdUrd) incorporated into DNA was used to estimate the number of 'repair patches' formed in response to a 254 nm UV (UVC) exposure. L5178Y-S cell, typical of rodent cell lines, formed a small number of patches in exposed DNA (1-2 patches per 1 x 108 dalton during a 6 h recovery after an exposure of 20 J/m2). In constrast, DNA extracted from L5178Y-R cells exposed to UVC and subsequently incubated with BrdUrd for 6 h showed no evidence of BrdUrd incorporation indicating no capacity to form sites of repair (fewer than 0.5 sites of BrdUrd incorporation per 1 x 108 dalton). Moreover, in L5178Y-R cells high fluences of UVC caused an extensive DNA degradation. Such degradation was not observed in L5178Y-S cells during the 24-h post-exposure period. These results are consistent with the notion that L5178Y-R cells have a reduced capacity to repair DNA damage induced by UVC radiation. (author)