Substrate proteins are linked to ubiquitin via lysine residues on the ubiquitin protein itself (Lys6, Lys11, Lys27, Lys29, Lys33, Lys48 and Lys63). Polyubiquitin chains are formed when a lysine residue of ubiquitin is linked to the carboxy-terminal glycine of another ubiquitin. Proteins poly-ubiquinated at specific lysine residues display a tendency to be targeted for different processes ranging from targeting of proteins to degradation in the proteasome, regulated function, subcellular localization, and influencing protein-protein interactions. Due to the limited tools available, the exact function of K6-poly-ubiquitination is largely unknown.