MMS21, also known as NSE2, is a SUMO ligase that in combination with the SMC5/6 complex is required for the prevention of DNA damage induced apoptosis by facilitating DNA repair in human cells. MMS21-dependent sumoylation is integral and important to the cohesion mechanism and mitotic progression, this function appears to be independent of SMC6. MMS21 mediates SUMO attachment to various proteins such as SMC6L1 and TRAX, and possibly the cohesin components RAD21 and STAG2.Synonyms: C8orf36, E3 SUMO-protein ligase NSE2, MMS21