EXCISION-REPAIR PATCH LENGTHS ARE SIMILAR FOR TRANSCRIPTION-COUPLED REPAIR AND GLOBAL GENOME REPAIR IN UV-IRRADIATED HUMAN-CELLS

We have used the buoyant density shift method to measure excision-repa ir patch lengths in W-irradiated repair-proficient human cells and in primary fibroblasts belonging to xeroderma pigmentosum complementation group C (XP-C), in which excision repair of UV-induced photoproducts is dependent upon transcription. The patch size was found to be about 30 nucleotides for both cell types. This agrees with the size of the D NA fragments excised in vitro by the dual incisions of the structure-s pecific nucleases XPG and ERCC1-XPF. We conclude that the XPC protein is not required to target the excision nucleases to sites of DNA cleav age in transcribed strands of expressed genes or to protect the newly incised DNA from further processing by exonucleases. (C) 1997 Elsevier Science B.V.