Ubiquitin-like protein modifier that can be covalently attached to lysine residues of target proteins. Activated by the dimeric UBA3-ULA1 E1 enzyme and conjugated by the E2 UBC12 to substrate proteins. RUB1-conjugated (neddylated) substrate proteins include the cullins CDC53, RTT101 and CUL3, and the modification enhances the ubiquitin-ligase activity of the corresponding cullin-RING-based E3 ubiquitin-protein ligase complexes (CRLs). Interacts with CDC53 and DCN1. Present with 1310 molecules/cell in log phase SD medium.