A fusion tag, called 3 × Flag-tag and consisting of eight amino acids (Met-Asp-Tyr-Lys-Asp-His-Asp-Gly-Asp-Tyr-Lys-Asp-His-Asp-Ile- Asp-Tyr-Lys-Asp-Asp-Asp-Asp-Lys) including an enterokinase-cleavage site, was specifically designed for immunoaffinity chromatography.

A fusion tag, called DYKDDDDK and consisting of eight amino acids (Asp-Tyr-Lys-Asp-Asp-Asp-Asp-Lys) including an enterokinase-cleavage site, was specifically designed for immunoaffinity chromatography.

The DYKDDDDK peptide has been used extensively as a general epitope tag in expression vectors. This peptide can be expressed and detected with the protein of interest as an amino-terminal or carboxy-terminal fusion.

Epitope tags are useful for the labeling and detection of proteins using immunoblotting,immunoprecipitation, and immunostaining techniques. Because of their small size, they are unlikely to affect the tagged protein’s biochemical properties.

Human influenza hemagglutinin (HA) is a surface glycoprotein required for the infectivity of the human virus. The HA tag derived from the HA molecule corresponding to amino acids 98-106 has been extensively used as a general epitope tag in expression vectors.