Repair of an interstrand DNA cross-link initiated by ERCC1-XPF repair/recombination nuclease

Interstrand DNA cross-link damage is a severe challenge to genomic integrit y. Nucleotide excision repair plays some role in the repair of DNA cross-li nks caused by psoralens and other agents. However, in mammalian cells there is evidence that the ERCC1-XPF nuclease has a specialized additional funct ion during interstrand DNA cross-link repair, beyond its role in nucleotide excision repair. We placed a psoralen monoadduct or interstrand cross-link in a duplex, 4-6 bases from a junction with unpaired DNA. ERCC1-XPF endonu cleolytically cleaved within the duplex on either side of the adduct, on th e strand having an unpaired 3' tail. Crosslinks that were cleaved only on t he 5' side were purified and reincubated with ERCC1-XPF, A second cleavage was then observed on the 3' side. Relevant partially unwound structures nea r a cross-link may be expected to arise frequently, for example at stalled DNA replication forks. The results show that the single enzyme ERCC1-XPF ca n release one arm of a cross-link and suggest a novel mechanism for interst rand cross-link repair.