Ubiquitin (Ub) is a 76 amino acid protein that is commonly found in isopeptide linkage to a lysine residue of a target protein. This post-translational modification controls most cellular processes, including DNA repair, trafficking and protein degradation. Ubiquitin conjugation onto any of its 7 own lysine residues or onto its N-terminus results in a large number of differently linked polymers; t ...