Neural Precursor Cell Expressed Developmentally Downregulated Gene 8 (NEDD8), also known as Rub1, is a 6-8 kDa member of the ubiquitin family of proteins. Human pro-NEDD8 is 81 amino acids (aa) in length. Pro-NEDD8 contains one ubiquitin-like domain (aa 1-65) and a 4-5 aa C-terminal propeptide. Cleavage of the propeptide exposes a C-terminal glycine residue that is used to generate a glycine-lysine intermolecular bond. Mature human NEDD8 shows 100% aa identity to NEDD8 from mouse, rat and canine. Human NEDD8 is activated by a distinct NEDD8-activating (E1) enzyme, a heterodimeric complex composed of APPBP1 and UBA3 subunits. Activated NEDD8 is subsequently transferred to the UBE2M/Ubc12 or UBE2F NEDD8-conjugating (E2) enzymes. Through a process termed neddylation, the ROC1/Rbx1 RING Finger E3 ligase transfers NEDD8 to specific substrates. For example, transfer of NEDD8 to the cullin scaffold activates members of the Cullin-RING Ligase (CRL) family of ubiquitin ligases (E3). CRL-induced ubiquitination is known to regulate proteins that are important for cell cycle progression and cell survival. Physiologically, NEDD8 plays a critical regulatory role in cell proliferation and dysregulation of the NEDD8 pathway has been associated with several cancer pathologies.