Free radical attack on the sugar-phosphate backbone generates oxidized apurinic/apyrimidinic (AP) residues in DNA. 2'-deoxyribonolactone (c[L) is a Cl'-oxidized AP site damage generated by UV and gamma-irradiation, and certain anticancer drugs. If not repaired dL produces G --> A transitions in Escherichia coli. In the base excision repair (BER) pathway, AP endonucleases are the major enzymes responsible for 5'-incision of the regular AP site (dR) and dL. DNA glycosylases with associated AP lyase activity can also efficiently cleave regular AP sites. Here, we report that dL is a substrate for AP endonucleases but not for DNA glycosylases/AP lyases. The kinetic parameters of the c[L-incision were similar to those of the dR. DNA glycosylases such as E coli formarniclopyrinlidine-DNA glycosylase, mismatch-specific Uracil-DNA glycosylase, and human alkylpurine-DNA N-glycosylase bind strongly to dL Without cleaving it. We show that dL cross-links with the human proteins 8-oxoguanine-DNA (hOGG1) and thymine glycol-DNA glycosylases (hNth1), and dR cross-links with Nth and hNth1. These results suggest that dL and dR induced genotoxicity might be strengthened by BER pathway in vivo. (C) 2005 Elsevier Inc. All rights reserved.