Component of the SMC5-SMC6 complex, a complex involved in repair of DNA double-strand breaks by homologous recombination. The complex may promote sister chromatid homologous recombination by recruiting the SMC1-SMC3 cohesin complex to double-strand breaks. The complex is required for telomere maintenance via recombination in ALT (alternative lengthening of telomeres) cell lines and mediates sumoylation of shelterin complex (telosome) components which is proposed to lead to shelterin complex disassembly in ALT-associated PML bodies (APBs). In vitro enhances ubiquitin ligase activity of NSMCE1. Proposed to act through recruitment and/or stabilization of the Ubl-conjugating enzyme (E2) at the E3:substrate complex (By similarity). May be a growth suppressor that facilitates the entry of the cell into cell cycle arrest (PubMed:14593116). Component of the SMC5-SMC6 complex which consists at least of SMC5, SMC6, NSMCE2, NSMCE1, NSMCE4A or EID3 and NSMCE3. NSMCE1, NSMCE4A or EID3 and NSMCE3 probably form a subcomplex that bridges the head domains of the SMC5:SMC6 heterodimer. Interacts with PJA1 (By similarity). Interacts with E2F1 (via C-terminus) (PubMed:14593116). Interacts with NGFR (via C-terminus) (PubMed:14593116). Interacts with NSMCE1. Interacts with NSMCE4. Interacts with SMC6. Interacts with EID3 (By similarity). Ubiquitous.