The SUMO ligase activity of the gene was inactivated by introduction of mutations encoding C195S and H197A in intron 6 and an FRT flanked pgk-neo cassette was inserted via homologous recombination. Flp mediated recombination removed the neo cassette. In vitro auto-SUMOylation assays confirmed the absence of SUMO ligase activity. However, protein levels and the stability of SMC5/6 complexes are similar to wild-type protein. (J:227197)