Holliday junction resolvase activity of human MUS81-EME2

Abstract

MUS81 is a highly conserved endonuclease with homology to the XPF subunit of the XPF-ERCC1 complex and catalytically active in a complex with a single regulatory subunit in lower eukaryotes, Mms4 and Eme1 in budding and fission yeasts, respectively, and two regulatory subunits, EME1 and EME2 in humans. In this study, we found that MUS81-EME2 is distinct from yeast Mus81-Mms4 and human MUS81-EME1, although they all share substrate specificity in common, cleaving various DNA structures including 3’ flaps, replication forks, and nicked Holliday junctions. We found that MUS81-EME2 only was able to resolve efficiently intact Holliday junctions unlike recombinant Mus81-Mms4. Furthermore, it was able to cleave nicked and gapped duplex DNA, generating two fragments. Ligatable nicks were significantly more resistant than nonligatable ones to the cleavage by MUS81-EME2, indicating its role in repair of abnormal DNA. Our biochemical data provide evidence that MUS81-EME2 alone could resolve Holliday junctions in higher eukaryotes such as mammals. This activity is in strong contrast to the nick-dependent cleavage of Holliday junctions by Mus81-Mms4 or MUS81-EME1. Our result raises the possibility that MUS81-EME1 and MUS81-EME2 are functionally distinct, playing related but non-overlapping roles in DNA transactions.