title: Effect of ultraviolet light on thymidine incorporation, DNA chain elongation and replicon initiation in wild-type and excision-deficient Chinese hamster ovary cells.
abstract: Wild-type Chinese hamster ovary cells (AA8) and five excision-deficient clones derived from the AA8 line (UV-4, UV-5, UV-20, UV-24 and UV-41) were exposed to ultraviolet light and then analyzed for their ability to incorporate [3H]thymidine and to initiate as well as elongate replicon-sized DNA fragments. After exposure to ultraviolet light, all cell lines exhibited a depression in the rate of thymidine incorporation. For exposures of 4.0 J/m2 or higher the wild-type cells recovered normal rates of thymidine incorporation within a few hours, while none of the excision-deficient lines exhibited complete recovery. For fluences below 4.0 J/m2 all but the UV-5 line exhibited at least some recovery. The ability to elongate DNA chains appeared to correlate with the thymidine incorporation data, with the UV-5 line exhibiting the strongest blockage of DNA chain elongation, the AA8 line exhibiting the least blockage, and the UV-20 line exhibiting an intermediate response. All cell lines exhibited a decrease in the distance between replication origins, thus supporting models which propose that exposure to ultraviolet light results in the use of alternative sites for the initiation of replication.
mesh_terms: D000818:Animals; D002460:Cell Line; D006224:Cricetinae; D003412:Cricetulus / Q000235:genetics; D011088:DNA Ligases / Q000235:genetics / Q000378:metabolism; D004260:DNA Repair; D004261:DNA Replication / Q000528:radiation effects*; D005260:Female; D005347:Fibroblasts / Q000378:metabolism; D007700:Kinetics; D010053:Ovary; D011740:Pyrimidine Dimers / Q000378:metabolism; D012093:Replicon; D013936:Thymidine / Q000378:metabolism; D014466:Ultraviolet Rays
chemical_list: D011740:Pyrimidine Dimers; D011088:DNA Ligases; D013936:Thymidine