Evidence for the excision repair of O6-n-butyldeoxyguanosine in human cells.

The persistence of O6-n-butyldeoxyguanosine (O6-nBudG) in DNA, the presence of O6-alkylguanine DNA alkyltransferase (AT) activity in cell extracts, and cell survival following exposure to N-n-butyl-N-nitrosourea (BNU), have been measured in normal and xeroderma pigmentosum cell strains, both transformed and untransformed. The rates of removal of O6-nBudG did not correlate with AT activity but did correlate with the ability of strains to excise bulky DNA lesions. BNU and N-methyl-N-nitrosourea dose-response curves for cell killing suggests that both AT and excision may be involved in the repair of cytotoxic lesions.