SUMO ligase activity of vertebrate Mms21/Nse2 is required for efficient DNA repair but not for Smc5/6 complex stability

► Nse2-deficient DT40 cells are viable, with reduced DNA repair capacity. ► Smc5, but not Smc6, was destabilised in the absence of Nse2. ► Nse2's SUMO ligase was required for efficient DNA repair, but not for Smc5 stability. ► Gel filtration analysis showed that Smc5 and Smc6 associate independently of Nse2. ► Nse2/Smc5 mutants are viable, with no significant increase in DNA damage sensitivity over the single Smc5 mutant.