XPF, also called DNA excision repair protein ERCC-4, or DNA repair protein complementing XP-F cells, or Xeroderma pigmentosum group F-complementing protein, is a 3'-flap repair endonuclease that cleaves 5' of ds/ssDNA interfaces in 3' flap structures, although it also cuts bubble, Y-DNA structures and mobile and immobile Holliday junctions. XPF cuts preferentially after pyrimidines, may continue to progressively cleave substrate upstream of the initial cleavage, at least in vitro. It may be involved in nucleotide excision repair. The nuclease domains of the catalytic subunits XPF have the GDX(n)ERKX(3)D motif which is required for metal-dependent endonuclease activity but not for DNA junction binding. XPF-ERRC1 and its yeast homolog Rad1-Rad10 play key roles in the excision of DNA lesions and are required for certain types of homologous recombination events and for the repair of DNA cross-links.