This linear ubiquitin fusion protein can be used as a substrate for deubiquitinating enzymes (DUBs) to test for non-isopeptide bond cleavage activity or preference. Ub is not expressed directly as free Ub but rather as linear fusions either to itself or to certain ribosomal protein subunits. These Ub-fusion precursors are proteolyzed by deubiquitinating enzymes (DUBs) at the appropriate junction points to yield active Ub monomers with C-termini ending in GG. There are likely several intracellular DUBs which perform this essential processing role. This protein can also be used to investigate mechanism of binding and recognition by E1 or E2 enzymes, DUBs, E3 ligases or other proteins that contain ubiquitin-associated domains (UBAs) or ubiquitin-interacting motifs (UIMs).