This fully functional N-terminal myc-tagged ubiquitin protein allows for the convenient detection or affinity purification of ubiquitinated proteins in vitro. The tag sequence (EQKLISEEDL) is an epitope derived from the C-terminal region of the human proto-oncoprotein p62^c-myc. This tag is specifically recognized by anti-myc antibodies or anti-myc-agarose. Ubiquitin is a 76 amino acid, highly conserved nuclear and cytoplasmic protein. It is found exclusively in eukaryotes, becomes covalently attached to substrate proteins by enzymes in the Ubiquitin-Proteasome Pathway (UPP) and has a major role in targeting cellular proteins for the ATP-dependent degradation by the 26S proteasome. Ubiquitination also affects proteasome-independent events such as protein localization, activity and function.