Accepts the ubiquitin-like protein NEDD8/RUB1 from the UBA3-ULA1 E1 complex and catalyzes its covalent attachment to other proteins. [E1 NEDD8-activating enzyme]-S-[NEDD8 protein]-yl-L-cysteine + [E2 NEDD8-conjugating enzyme]-L-cysteine = [E1 NEDD8-activating enzyme]-L-cysteine + [E2 NEDD8-conjugating enzyme]-S-[NEDD8-protein]-yl-L-cysteine. Protein modification; protein neddylation. Belongs to the ubiquitin-conjugating enzyme family. UBC12 subfamily.