The function of ENSG00000144744 (UBA3, ubiquitin like modifier activating enzyme 3) is as follows. Catalytic subunit of the dimeric UBA3-NAE1 E1 enzyme. E1 activates NEDD8 by first adenylating its C-terminal glycine residue with ATP, thereafter linking this residue to the side chain of the catalytic cysteine, yielding a NEDD8-UBA3 thioester and free AMP. E1 finally transfers NEDD8 to the catalytic cysteine of UBE2M. Down- regulates steroid receptor activity. Necessary for cell cycle progression. {ECO:0000269|PubMed:10207026, ECO:0000269|PubMed:12740388, ECO:0000269|PubMed:9694792}.