Ubiquitin-like (UBL) post-translational modifiers are covalently linked to most, if not all, target protein(s) through an enzymatic cascade analogous to ubiquitylation, consisting of E1 (activating), E2 (conjugating), and E3 (ligating) enzymes. Ubiquitin-fold modifier 1 (Ufm1) a ubiquitin-like protein is activated by a novel E1-like enzyme, Uba5, by forming a high-energy thioester bond. Activated Ufm1 is then transferred to its cognate E2-like enzyme, Ufc1, in a similar thioester linkage. This family represents the E2-like enzyme.

1: A novel protein-conjugating system for Ufm1, a ubiquitin-fold modifier. Komatsu M, Chiba T, Tatsumi K, Iemura S, Tanida I, Okazaki N, Ueno T, Kominami E, Natsume T, Tanaka K; EMBO J. 2004;23:1977-1986. PMID:15071506