X-ray repair cross-complementing gene I protein (XRCC1) in complex with DNA polymerase beta, DNA ligase III, and poly(ADP-ribose) polymerase is important in the base excision repair process. Previously, we isolated camptothecin (CPT)-resistant cell lines (KB100 and KB300) from the human epidermoid carcinoma cell line KB by exposure to CPT. From these CPT-resistant cell lines, their revertants (...