Structure‐Specific Endonuclease XPF‐ERCC1 Plays a Critical Role in DNA Interstrand Crosslink Repair That is Compromised in Patients with Fanconi Anemia

DNA repair is a critical process to prevent genomic instability, a hallmark of cancer. DNA interstrand crosslinks (ICLs) may occur spontaneously via endogenous cellular components or exogenous DNA damaging agents such as the platinum drugs. Because DNA replication is blocked as a result of crosslinks, genomic integrity may be compromised and cell death may occur if replication fork stalling is not resolved. The structure‐specific endonuclease XPF‐ERCC1 has been reported to be a crucial component for this kind of lesion repair. Mutations in XPF have also been described that give rise to Fanconi Anemia, a childhood disorder characterized by developmental problems, bone marrow dysfunction and a high predisposition to early development of cancer. Using the yeast homolog to XPF‐ERCC1, Rad1‐Rad10, we focus on the functions of XPF‐ERCC1 that are specific for ICL repair and separate the distinct nuclease activities in yeast. We show that this complex is directly involved in 3' flap removal during ICL repair, and that this activity is redundant with another endonuclease, Mus81‐Mms4, in repairing interstrand crosslinks. In addition, we show that mutations in Rad1 which mimic XPF mutations in patients with Fanconi Anemia are sensitive to ICL damage. Our results indicate that XPF‐ERCC1 has specific roles throughout ICL repair and that this endonuclease employs separate nuclease functions to resolve DNA interstrand crosslink lesions in both yeast and mammals. Furthermore, we propose that deficiency in 3' flap removal leads to Fanconi Anemia, thus emphasizing its critical role in suppressing a cancer predisposition.