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. Necessary for cell cycle progression through the S-M checkpoint. Overexpression of NAE1 causes apoptosis through deregulation of NEDD8 conjugation. Binding of TP53BP2 to the regulatory subunit NAE1 decreases neddylation activity. Protein modification; protein neddylation. Heterodimer of UBA3 and NAE1. The complex binds NEDD8 and UBE2M. Binds APP and TP53BP2. Colocalizes with APP in lipid rafts. Ubiquitous in fetal tissues. Expressed throughout the adult brain. Ubiquitinated by TRIP12, leading to its degradation by the proteasome. NAE1 and UBA3 correspond to the N-terminal and the C-terminal part of yeast UBA3. In yeast the two subunits form a single polypeptide chain. Belongs to the ubiquitin-activating E1 family. ULA1 subfamily.