title: Enhancement of excision-repair efficiency by conditioned medium from density-inhibited cultures in V79 Chinese hamster cells: evidence for excision repair as an error-free repair process.
abstract: Conditioned medium from density-inhibited V79 Chinese hamster cell cultures, given as a post-treatment to UV-irradiated homologous cells, was demonstrated to reduce the lethal action of ultraviolet light by temporarily blocking DNA replication. Since the increased survival was not affected by various non-toxic concentrations of caffeine, such protective effect would be attributable to the prolonged intervention of excision repair before DNA replication during the post-treatment period. The influence of conditioned medium on the UV-induced mutation at the ouabain-resistance locus was also examined and a significant decrease in mutation frequency was noted. The observed reduction in killing and mutation as a result of post-incubation in conditioned medium, which delays DNA replication, would be interpreted as evidence that conditioned medium provides a longer period of time for an error-free excision-repair process, leaving lesion in DNA available for error-prone post-replication repair.
mesh_terms: D000818:Animals; D002460:Cell Line; D006224:Cricetinae; D003470:Culture Media / Q000494:pharmacology*; D004247:DNA / Q000528:radiation effects; D004260:DNA Repair / Q000187:drug effects*; D008168:Lung; D014466:Ultraviolet Rays
chemical_list: D003470:Culture Media; D004247:DNA