DNA repair of benzo[a]pyrene diol epoxide-DNA adducts in the DHFR gene of a human embryonic kidney cell line.

The repair of polycyclic aromatic hydrocarbon (PAH)-DNA adducts by nucleoti de excision repair isa critical factor in the human response to exposure to these environmental carcinogens. In this study, we utilized a Laser cleava ge technique and Southern Blotting to measure the repair of benzo[a]pyrene- 7,8-diol-9, 10-epoxide (BPDE) adducts in the transcribed and nontranscribed strands of a human cell line containing an amplified DHFR gene. Treatment of the cultures with 1.5 mu M BPDE resulted in little adduct removal for 24 hours, whereas 1 mu M BPDE-treated cells removed most of the adducts over a 24 hour period. Southern analyses of repair in individual strands of the human cell line revealed that adducts on the transcribed strand are repaire d more rapidly than those on the non-transcribed strand during the first 8 hours after 1 mu M BPDE treatment. These results suggest that human cells c an repair BPDE-DNA adducts through a transcription-coupled repair process.