title: Loss of DNA repair capacity during successive subcultures of primary rat fibroblasts.
abstract: Cultures of fibroblasts from newborn rats and successive subcultures of these cells were treated with 4-nitroquinoline-1-oxide to induce DNA repair. DNA from the cultures was examined by velocity sedimentation in alkaline sucrose gradients immediately after drug treatment and after a post-treatment incubation period of 3 h. Early passage cells were able to repair the damage that appeared as single strand breaks, however, by the seventh subculture this activity was not apparent. Measurements of repair synthesis showed a partial loss of this capacity with successive subculture. The results fit a model in which 4NQO causes two kinds of DNA modification, one of which is alkali labile and appears as a single-strand break. Both modifications are subject to excision repair, but each is recognized initially by a specific endonuclease. In the late passage cells, the endonuclease specific for the alkali labile modification is absent.
mesh_terms: D015112:4-Nitroquinoline-1-oxide / Q000494:pharmacology; D000818:Animals; D046508:Culture Techniques; D004247:DNA / Q000096:biosynthesis*; D004260:DNA Repair; D005347:Fibroblasts / Q000187:drug effects / Q000378:metabolism*; D051381:Rats
chemical_list: D015112:4-Nitroquinoline-1-oxide; D004247:DNA