E1-like enzyme which specifically catalyzes the first step in ufmylation. Activates UFM1 by first adenylating its C-terminal glycine residue with ATP, and thereafter linking this residue to the side chain of a cysteine residue in E1, yielding a UFM1-E1 thioester and free AMP. Activates UFM1 via a trans-binding mechanism, in which UFM1 interacts with distinct sites in both subunits of the UBA5 homodimer. Trans-binding also promotes stabilization of the UBA5 homodimer, and enhances ATP-binding. Transfer of UFM1 from UBA5 to the E2-like enzyme UFC1 also takes place using a trans mechanism. Ufmylation is involved in reticulophagy (also called ER-phagy) induced in response to endoplasmic reticulum stress (By similarity). Ufmylation is essential for erythroid differentiation of both megakaryocytes and erythrocytes (By similarity).
Subcellular locations: Cytoplasm, Nucleus, Endoplasmic reticulum membrane, Golgi apparatus
Localizes mainly in the cytoplasm, while it localizes to the nucleus in presence of SUMO2. Interaction with GABARAPL2 promotes localization to the endoplasmic reticulum membrane.