The 2 SUMO consensus sites (K119 and K194) in exon 3 were mutated to arginine (R) residues and a floxed neo cassette was inserted downstream of exon 3 via homologous recombination. Cre mediated recombination removed the neo cassette. Tissues in homozygous mice showed a pronounced loss of sumoylated protein species. (J:175843)