Ufm1

Ufm1 (Ubiquitin-fold modifier 1) is a recently identified ubiquitin-like protein (Ubl) based on the similarity of its tertiary structure to ubiquitin (Ub). Similar to Ub and other Ubls, Ufm1 is conjugated to cellular proteins via its C-terminal Gly residue by sequential action of the Ufm1-activating enzyme Uba5, the Ufm1-conjugating enzyme Ufc1, and the Ufm1 ligase Ufl1. Ufm1 conjugation is reversible and the release of free Ufm1 from target proteins is carried out by two Ufm1-specific proteases, UfSP1 and UfSP2. These UfSPs are also responsible for the generation of mature form of Ufm1 from its precursors. The Ufm1 conjugation and deconjugation systems are well conserved from C. elegans to human (but not in yeast or prokaryotes), implicating their critical role in multicellular organisms. However, target proteins for Ufm1 modification and the role of this conjugation system remain totally unknown.