Component of the SMC5-SMC6 complex, a complex involved in repair of DNA double-strand breaks by homologous recombination (PubMed:23555814). The complex may promote sister chromatid homologous recombination by recruiting the SMC1-SMC3 cohesin complex to double-strand breaks (By similarity). S-ubiquitinyl-[E2 ubiquitin-conjugating enzyme]-L-cysteine + [acceptor protein]-L-lysine = [E2 ubiquitin-conjugating enzyme]-L-cysteine + N(6)-ubiquitinyl-[acceptor protein]-L-lysine. Component of the Smc5-Smc6 complex which consists at least of Smc5, Smc6, Nse1, Nse2, Nse4 and MAGE. Nse1, Nse4 and MAGE probably form a subcomplex that bridges the head domains of the Smc5-Smc6 heterodimer (By similarity). Interacts with MAGE and Nse4. Belongs to the NSE1 family.