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.