Acts in a DNA repair pathway for removal of UV-induced DNA damage that is distinct from classical nucleotide excision repair and in repair of ionizing radiation damage. Functions in homologous recombination repair of DNA double strand breaks and in recovery of stalled replication forks. Plays a critical role in meiosis. Two subcomplexes smc5-smc6-nse2 and nse1-nse3-nse4 exist. These subcomplexes are then brought together via a number of interactions, forming the Smc5-Smc6 complex. Belongs to the NSE4 family.