Linkage specific penta-Ub can be used to investigate mechanism of binding and recognition by E1 or E2 enzymes, deubiquitinating enzymes, E3 ligases, the proteasome or other proteins that contain ubiquitin-associated domains (UBAs) or ubiquitin-interacting motifs (UIMs). This product is formed with wild-type ubiquitin and linkage-specific enzymes. It has been shown that the rate of ubiquitin-substrate conjugate degradation is related to polyubiquitin chain length. Tetra-ubiquitin is the minimal unit required for recognition by the proteasome, and longer chains probably have enhanced binding to proteasomal subunits and may be more resistant to disassembly by a proteasome-associated isopeptidases.