[Isoform 1]: Non-catalytic component of a structure-specific DNA repair endonuclease responsible for the 5'-incision during DNA repair. Responsible, in conjunction with SLX4, for the first step in the repair of interstrand cross-links (ICL). Participates in the processing of anaphase bridge-generating DNA structures, which consist in incompletely processed DNA lesions arising during S or G2 phase, and can result in cytokinesis failure. Also required for homology-directed repair (HDR) of DNA double-strand breaks, in conjunction with SLX4; [Isoform 2]: Not functional in the nucleotide excision repair pathway; [Isoform 3]: Not functional in the nucleotide excision repair pathway; [Isoform 4]: Not functional in the nucleotide excision repair pathway.