Linkage specific poly-ubiquitin chains are used to investigate mechanisms of chain recognition, binding and hydrolysis by the proteasome, deubiquitinating enzymes, E3 ligases or other proteins that contain ubiquitin-associated domains or ubiquitin-interacting motifs (UIMs). This product is formed with wild-type human recombinant ubiquitin and linkage-specific enzymes.  This mixture of poly-ubiquitin chains contains di-ubiquitin and higher MW species; mono-ubiquitin has been removed. These chains have been modified with biotin via primary amine coupling.  This results in multiple biotinylated species modified at the N-terminus, as well as lysine residues.  Biotinylated ubiquitin can be detected using avidin-linked reagents.