title: Effect of ultraviolet light on DNA replication in excision-deficient mammalian cells.
abstract: DNA replication after exposure to 254-nm ultraviolet light was examined in wild-type (AA8) and excision-deficient (UV-5) Chinese hamster ovary (CHO) cells. DNA replication was examined by measuring the incorporation of [3H]thymidine into acid-precipitable form and by DNA fiber autoradiography. Following exposure to UV both cell lines exhibited a fluence-dependent reduction in the rate of incorporation of thymidine. For exposures of 3.25 and 6.5 J/m2 the response was quantitatively similar in both cell lines for the first hour or two following exposure, with thymidine incorporation dropping to less than 50% of the control rate within the first 1-2 h. For the AA8 cells the depression was only temporary with the rate of thymidine incorporation eventually recovering to control levels. UV-5 cells, on the other hand, never exhibited a recovery in the rate of thymidine incorporation, even at a fluence as low as 0.8 J/m2. DNA fiber-autoradiographic analysis revealed that for both AA8 and UV-5 lines there were about a 40% reduction in the rate of chain growth in the first 40 min after exposure to 6.5 J/m2. The rate of DNA chain elongation recovered to normal rates in less than 5 h in AA8 cells while little or no recovery in the rate of DNA chain elongation was observed for up to 5 h in the UV-5 cells. From these results it appears that the steps of excision repair that are missing in the UV-5 cells are required not only for excision repair, but also for the ability of cells to recover normal rates of DNA replication following exposure to UV.
mesh_terms: D000818:Animals; D001345:Autoradiography; D002460:Cell Line; D006224:Cricetinae; D003412:Cricetulus; D004261:DNA Replication / Q000528:radiation effects*; D004307:Dose-Response Relationship, Radiation; D005260:Female; D007700:Kinetics; D009154:Mutation; D010053:Ovary; D013936:Thymidine / Q000378:metabolism; D014316:Tritium; D014466:Ultraviolet Rays
chemical_list: D014316:Tritium; D013936:Thymidine