| The interaction between Wrn and SUMO 1 was weaker than that between Wrn and Ubc 9 . ^^^ Positive interaction was observed in the heterogeneous combination of Wrn and yeast Ubc 9 ( yUbc 9 ) , as well as yUbc 9 and SUMO 1 , in the two hybrid system . ^^^ The interaction of Wrn and SUMO 1 was also abolished by deleting the Gly residue , indicating that the interaction of Wrn and SUMO 1 is mediated by yUbc 9 in the two hybrid system . ^^^ Finally , we confirmed by immunoblotting with an anti SUMO 1 antibody that Wrn was covalently attached with SUMO 1 . . ^^^ |