Epitope tags provide a method to localize gene products in a variety of cell types, study the topology of proteins and protein complexes, identify associated proteins, and characterize newly identified, low abundance or poorly immunogenic proteins when protein specific antibodies are not available. Expression of recombinant proteins in E.Coli is a fusion protein with neighboring histidine residues is one of the most popular methods of epitope tags.

The affinity of the histidine-tag motif to Ni2+ by chelation is strong and selective enough to enable purification of the protein to homogeneity by affinity chromatography on a Ni2 +/- NTA ad -sorbent.