Core 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). Forms a heterodimer with smc5. Component of the SMC5-SMC6 complex which consists at least of smc5, smc6, nsmce2, nsmce1 and nsmce4a (By similarity). Associates with chromatin. Loaded onto chromatin during DNA replication in a manner dependent on the initiation of DNA synthesis, and it dissociated from chromatin during mitosis. Chromatin loading is not induced by DNA double-strand breaks. The flexible hinge domain, which separates the large intramolecular coiled coil regions, allows the heterotypic interaction with the corresponding domain of SMC5, forming a V-shaped heterodimer. Belongs to the SMC family. SMC6 subfamily.