REPAIR OF THYMINE DIMERS AND (6–4) PHOTOPRODUCTS IN GROUP A XERODERMA PIGMENTOSUM CELL LINES HARBORING A TRANSFERRED NORMAL CHROMOSOME 9

Abstract
—: Transfer of a normal chromosome 9 into a xeroderma pigmentosum (XP)‐A cell line partially restored its DNA repair activity. XP‐A cell lines harboring a transferred chromosome were much more UV‐resistant than parental XP‐A cells but still more UV‐sensitive than normal cells. The amount of UV‐induced unscheduled DNA synthesis was only one‐third of that in normal cells. The repair of thymine dimers and (6–4) photoproducts in these cell lines was analyzed by using monoclonal antibodies raised against them. Although these XP‐A cell lines carrying a normal chromosome 9 could repair (6–4) photoproduct with a little lower efficiency than normal cells, the repair of thymine dimers was completely absent in these cells. The present results suggest a gene‐dosage effect in DNA excision repair mechanisms in human cells or a rather complicated mechanism which involves two or more pathways.

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