A member of the E2/UBC superfamily of proteins found in several bacteria. Members of this family lack the conserved histidine of the classical E2-fold. However, they have an absolutely conserved histidine carboxyl-terminal to the conserved cysteine [1,2]. Members of this family are usually present in a conserved gene neighborhood with genes encoding members of the Ub modification pathway such as the E1, Ub and JAB proteins. These neighborhoods also contain a gene encoding a rapidly diverging alpha-helical protein [1].

1: The prokaryotic antecedents of the ubiquitin-signaling system and the early evolution of ubiquitin-like beta-grasp domains. Iyer LM, Burroughs AM, Aravind L; Genome Biol. 2006;7:R60. PMID:16859499

2: Anatomy of the E2 ligase fold: implications for enzymology and evolution of ubiquitin/Ub-like protein conjugation. Burroughs AM, Jaffee M, Iyer LM, Aravind L; J Struct Biol. 2008;162:205-218. PMID:18276160