Catalytic subunit of the dimeric UBA3-ULA1 E1 enzyme. E1 activates NEDD8/RUB1 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 UBC12. ATP + [NEDD8 protein] + [E1 NEDD8-activating enzyme]-L-cysteine = AMP + diphosphate + [E1 NEDD8-activating enzyme]-S-[NEDD8 protein]-yl-L-cysteine. Protein modification; protein neddylation. Heterodimer of UBA3 and ULA1. Interacts with NEDD8 and UBC12 (By similarity). Present with 752 molecules/cell in log phase SD medium. Belongs to the ubiquitin-activating E1 family. UBA3 subfamily.