NEDD8 (Neural precursor cell-expressed developmentally down-regulated gene 8, also known as Rub1) is a 6-8 kDa member of the ubiquitin family of proteins. It is expressed in striated muscle, and via its C-terminal Gly, forms covalent bonds with cullin family proteins. This conjugation generates ubiquitin ligase activity that regulates cell cycle proteins. Human pro-NEDD8 is 81 amino acids (aa) in length. It contains one ubiquitin-like domain (aa 1-65), and a 4-5 aa C-terminal propeptide that is cleaved to expose a C-terminal Gly residue that is used to generate a Gly-Lys intermolecular bond. Mature human NEDD8 shows 100% aa identity to NEDD8 from both mouse and canine.