Abstract
DNA double-strand breaks (DSBs) with 5' adducts are frequently formed from many nucleic acid processing enzymes, in particular DNA topoisomerase 2 (TOP2). The key intermediate of TOP2 catalysis is the covalent complex (TOP2cc), consisting of two TOP2 subunits covalently linked to the 5' ends of the nicked DNA. In cells, TOP2ccs can be trapped by cancer drugs such as etoposide and then converted into DNA double-strand breaks (DSBs) that carry adducts at the 5' end. The repair of such DSBs is critical to the survival of cells, but the underlying mechanism is still not well understood. We found that etoposide-induced DSBs are efficiently resected into 3' single-stranded DNA in cells and the major nuclease for resection is the DNA2 protein. DNA substrates carrying model 5' adducts were efficiently resected in Xenopus egg extracts and immunodepletion of Xenopus DNA2 also strongly inhibited resection. These results suggest that DNA2-mediated resection is a major mechanism for the repair of DSBs with 5' adducts.