E1-like enzyme which activates UFM1. Interacts (via C-terminus) with Ufc1. Interacts with Ufm1. RNAi-mediated knockdown shows aberrant neuromuscular junctions in the larval muscle and abnormal wings, locomotive defects and a shortened lifespan in the adult fly. RNAi-mediated knockdown in the nervous system results also in aberrant neuromuscular junctions characterized by reduced number of type Ib boutons and increased bouton size in the larval muscle. Belongs to the ubiquitin-activating E1 family. UBA5 subfamily.