ERCC1-XPF endonuclease-positioned to cut

Abstract

To counteract damage to our genomes, numerous endo‐ and exonucleases incise the DNA backbone to remove damaged and aberrant DNA structures. It is imperative that such incisions be very tightly controlled, as unwanted DNA breaks are a key source of genome instability. Two new papers in The EMBO Journal shed light on how the activity of one such nuclease—ERCC1‐XPF, an enzyme involved in various DNA repair pathways—is regulated to perform incision in the vicinity of DNA interstrand crosslinks.

Figure 1. Interactions of ERCC1‐XPF in NER and ICL repair

(A) ERCC1‐XPF heterodimerizes via the C‐terminal HhH domains. The central domain of ERCC1 mediates the interaction with XPA in NER and mutations in residues N110 and Y145 compromise the NER activity of ERCC1‐XPF (shown in red). The nuclease domain in XPF contains the active site residues. Mutation of residues R689 and S786 does not affect the catalytic mechanism, but alters DNA binding in the nuclease domain and leads to an ICL repair‐specific defect (shown in green). The helicase‐like domain (HLD) of XPF interacts with SLX4 and likely RPA. Mutation of residue L230 abolishes ICL repair and SLX4 binding; deletion of residues 323–326 abolishes ICL repair, but retains binding affinity for SLX4 (shown in green). This region may mediate an interaction with SLX4 that is needed for the proper positioning of XPF at sites of ICL repair. The interaction with RPA is required for NER and ICL repair, but the exact location of the RPA binding site in the HLD remains to be determined. (B) The XPA protein recruits ERCC1‐XPF to NER complexes, SLX4 to sites of ICL repair. RPA positions ERCC1‐XPF for incision in NER and ICL repair by binding ssDNA with a defined polarity at the junction to position ERCC1‐XPF for incision. The role of RPA is conserved between the two pathways.