Regulatory 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 (By similarity). Protein modification; protein neddylation. Heterodimer of UBA3 and NAE1. The complex binds NEDD8 and UBE2M (By similarity). Belongs to the ubiquitin-activating E1 family. ULA1 subfamily.