Regulatory subunit of the dimeric uba-3-ula-1 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-rfl-1 (uba-3) thioester and free AMP. E1 finally transfers NEDD8 to the catalytic cysteine of ubc-12 (PubMed:10993680). Required for rfl-1 (uba-3) nuclear localization during early embryonic development (PubMed:19528325). Protein modification; protein neddylation. Heterodimer of uba-3 and ula-1. The complex binds NEDD8 and ubc-12 (By similarity). RNAi-mediated knockdown causes the formation of an everted vulva in the L4 stage, with the subsequent rupture of the animal during the L4-to-adult molt (PubMed:10993680). Loss of rfl-1 nuclear localization in a 1- to 2-cell embryonic stages (PubMed:19528325). Belongs to the ubiquitin-activating E1 family. ULA1 subfamily.