Component of a DNA structure-specific endonuclease with substrate preference for branched DNA structures with a 5'-end at the branch nick. May be required in mitosis for the processing of stalled or collapsed replication fork intermediates. May be required in meiosis for the repair of meiosis-specific double strand breaks subsequent to single-end invasion (SEI) (By similarity). Interacts with eme1. Belongs to the XPF family.