DNA repair in the genomic region containing the beta-actin gene in xeroderma pigmentosum complementation group C and...

The limited DNA excision repair in UV-irradiated fibroblasts from xeroderma pigmentosum complementation group C (XP-C) occurs in selected chromatin regions. The small beta-actin gene (3.5 kb) is one of these and is repaired as part of a large region (about 50 kb). We show here that only one of the DNA strands is repaired through this extended region. Several genomic fragments spanning about 70 kb in the beta-actin region have been cloned and mapped and some have been examined for repair activity. Both strands of one fragment (14 kb) in the immediate vicinity of the gene are repaired. Transcripts associated with both strands are detected. In normal cells, both strands of the same fragment are preferentially repaired relative to the genome overall and also associated with transcription. The repair activity in XP-C cells associated with other defined DNA fragments indicates that termini for the repaired regions in either strand can be located. Results are consistent with those of others indicating that transcription promotes repair in XP-C cells and that several levels of repair activity, at least one coupled to transcription, occur in normal cells. We conclude that the beta-actin repair domain, defined in XP-C cells, comprises both strands of a small region (about 14 kb) in the vicinity of the beta-actin gene and a single strand extending through a larger region of about 50 kb. We suggest that a similar genomic organization for repair exists in normal cells.