FLAG-tag stands for an octapeptide with a sequence of DYKDDDDK. It is a polypeptide protein tag that can be added to a protein using recombinant DNA technology. It is widely used for affinity chromatography to purify recombinant proteins from variety of systems. It can also be used in the isolation of protein complexes with multiple subunits. A FLAG-tag can be used in many different assays that require recognition by an antibody. If there is no antibody against the studied protein, adding a FLAG-tag to this protein allows one to follow the protein with an antibody against the FLAG sequence, such as in ELISA, Western Blot, etc.