Linkage specific, non-hydrolyzable tetra-ubiquitin is resistant to the activity of enzymes (DUB's) that cleave the isopeptide linkage between adjacent ubiquitin molecules.  It can be used to investigate binding interactions between tetra-ubiquitin and proteins that contain elements such as ubiquitin-associated domains (UBA's), ubiquitin-interacting motifs (UIM's) and CARD domains.  This product may also be useful in exploring the role of unanchored poly-ubiquitin chains in some signaling pathways.