Ub chains are formed by conjugating the C-terminal glycine residue of Ub onto any of seven internal lysine residues or the amino group of the previous Ub. Ub chains are classified by the lysine residue used to link Ubs; different Ub chain topologies can result in different signals. For instance, Ub chains linked through lysine 6, 11, 27, 29, 33 and 48 are capable of targeting proteins for proteasomal degradation; in contrast, Ub chains linked through lysine 63 or the N-terminal amino group (linear Ub chains) often play important nonproteolytic functions including regulation of kinase activation and protein translation. All Ub chain products are produced by using of human wild type Ub reacting with specific E2s.
