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. May prevent formation of excessive Holliday junctions or assist in their resolution. Component of the smc5/smc6 complex which consists of two subcomplexes, smc5-smc6-nse2 and nse1-nse2-nse4. Interacts with nse6 and rfp1.