| Modification of Msx 1 by SUMO 1 . ^^^ We show that Msx 1 conjugation to SUMO 1 in vivo is enhanced by an E 3 SUMO ligase , PIAS 1 , suggesting that sumoylation of Msx 1 is a new mechanism for modulating the molecular function of Msx 1 during organogenesis . . ^^^ |