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 and mediates sumoylation of shelterin complex (telosome) components (By similarity). 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 NSMCE3. Belongs to the NSE4 family.