InterPro domain: IPR045132

E4 is an ubiquitin chain-elongation enzyme specifically involved in polyubiquitin chain assembly. It is involved in N-terminal ubiquitin fusion degradation proteolytic pathway (UFD pathway). E4 binds to the ubiquitin moieties of preformed conjugates and catalyses ubiquitin chain assembly in conjunction with E1, E2, and E3. E4 appears to influence the formation and topology of the multi-Ub chain as it enhances ubiquitination at 'Lys-48' but not at 'Lys-29' of the N-terminal Ub moiety [ 1 ].

1. Definitive evidence for Ufd2-catalyzed elongation of the ubiquitin chain through Lys48 linkage. Biochem Biophys Res Commun 320, 840-5