IUBMB Enzyme Nomenclature


Accepted name: (E3-independent) E2 ubiquitin-conjugating enzyme

Reaction: S-ubiquitinyl-[E1 ubiquitin-activating enzyme]-L-cysteine + [acceptor protein]-L-lysine = [E1 ubiquitin-activating enzyme]-L-cysteine + N6-monoubiquitinyl-[acceptor protein]-L-lysine (overall reaction)
(1a) S-ubiquitinyl-[E1 ubiquitin-activating enzyme]-L-cysteine + [(E3-independent) E2 ubiquitin-conjugating enzyme]-L-cysteine = [E1 ubiquitin-activating enzyme]-L-cysteine + S-monoubiquitinyl-[(E3-independent) ubiquitin-conjugating enzyme]-L-cysteine
(1b) S-monoubiquitinyl-[(E3-independent) E2 ubiquitin-conjugating E2 enzyme]-L-cysteine + [acceptor protein]-L-lysine = [(E3-independent) E2 ubiquitin-conjugating enzyme]-L-cysteine + N6-monoubiquitinyl-[acceptor protein]-L-lysine

Other name(s): E2-230K; UBE2O; E3-independent ubiquitin-conjugating enzyme E2

Systematic name: S-ubiquitinyl-[E1 ubiquitin-activating enzyme]-L-cysteine:L-lysine ubiquitinyl transferase ([E3 ubiquitin transferase]-independent)

Comments: The enzyme transfers a single ubiquitin directly from an ubiquitinated E1 ubiquitin-activating enzyme to itself, and on to a lysine residue of the acceptor protein without involvement of E3 ubiquitin transferases (cf. EC, EC It forms a labile ubiquitin adduct in the presence of E1, ubiquitin, and Mg2+-ATP and catalyses the conjugation of ubiquitin to protein substrates, independently of E3. This transfer has only been observed with small proteins. In vitro a transfer to small acceptors (e.g. L-lysine, N-acetyl-L-lysine methyl ester) has been observed [1].

Links to other databases: BRENDA, EXPASY, KEGG, MetaCyc, CAS registry number:


1. Pickart, C.M. and Rose, I.A. Functional heterogeneity of ubiquitin carrier proteins. J. Biol. Chem. 260 (1985) 1573-1581. [PMID: 2981864]

2. Hoeller, D., Hecker, C.M., Wagner, S., Rogov, V., Dotsch, V. and Dikic, I. E3-independent monoubiquitination of ubiquitin-binding proteins. Mol. Cell 26 (2007) 891-898. [PMID: 17588522]

3. Ramanathan, H.N., Zhang, G. and Ye, Y. Monoubiquitination of EEA1 regulates endosome fusion and trafficking. Cell Biosci 3 (2013) 24. [PMID: 23701900]

[EC created 2015]

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