Interacts with MUS81 to form a DNA structure-specific endonuclease with substrate preference for branched DNA structures with a 5'-end at the branch nick. Typical substrates include 3'-flap structures, replication forks and nicked Holliday junctions. May be required in mitosis for the processing of stalled or collapsed replication forks. May self-associate (By similarity). Interacts with MUS81. Recruited to regions of DNA damage in S-phase cells. Weakly expressed in brain, heart, kidney, liver, lung, muscle, skin, small intestine, spleen, stomach, testis and thymus (PubMed:14609959, PubMed:27010503). Expressed in bone marrow (PubMed:27010503). Also expressed in embryonic stem cells (ES cells) (PubMed:14609959). Belongs to the EME1/MMS4 family.