XPF forms a heterodimeric complex with ERCC1 and is required for the repair of DNA interstrand cross-links. In association with ERCC1, it is involved in production of the 5′ incision at the site of a psoralen interstrand cross-link as well as the 3′ incision. The present study was carried out to determine the functional domains of XPF that are important in the production of the 5′ and 3′ incisions that occur at a site of a psoralen interstrand cross-link. Monoclonal antibodies (mAbs) were utilized that had been generated against polypeptide fragments of XPF and affinity-mapped to specific regions of XPF. These mAbs were examined for their ability to differentially inhibit production of dual incisions in DNA by normal human chromatin-associated protein extracts that contain XPF and ERCC1. These studies show that two regions of XPF, one N-terminal region from amino acids 12-166 and one C-terminal region from amino acids 702-854, are the most important in the production of the 5′ incision. The same N-terminal region and the C-terminal region from amino acids 702-916 are also involved in the 3′ incision, though to a much lesser extent. Since this C-terminal region corresponds to the proposed site of interaction of ERCC1 with XPF, these results suggest that binding of ERCC1 to XPF is critical for its ability to produce the 5′ and 3′ incisions at the site of an interstrand cross-link, possibly through activation or regulation of the endonucleolytic activity of the N-terminal domain of XPF.
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