MOLECULAR BIOLOGY OF CELLULAR INJURY

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Several inducible DNA repair genes have been well characterized in prokaryotic systems; in eukaryotes including mammalian cells, there is increasing evidence that similar events may be occurring. Recently, we have shown that hybridization subtraction can be used to enrich for sequences induced only several fold by a particular cell treatment such as heat shock. Chinese hamster cells were UV-irradiated and cDNA was synthesized from the polyadenylated (polyA) RNA of these cells. This "UV" cDNA was hybridized with polyA RNA from unirradiated cells and the nonhybridizing cDNA was isolated. With this approach, UV- induced sequences were enriched for over 30 fold. With this enriched cDNA, a cDNA library was constructed. 50 different cDNA clones were isolated which were found to code for transcripts induced 2 to 30 fold after UV. 27 different cDNA clones were sequenced and only metallothionein was identified in the GenBank database which indicates that most of these sequences have not been isolated before. In preliminary experiments, several of these clones were found to hybridize to UV-inducible transcripts in human fibroblasts. In Chinese hamster somatic cell mutants selected for increased sensitivity to DNA damaging agents by I. Hickson, several examples of both increased and decreased transcription in the mutant cells were found. The function of these cloned sequences is unknown, but it is probable that the protein products of at least some of these transcripts play a role in the cellular response to UV damage.