||The DYKDDDDK (FLAG) peptide has been used extensively as a general tag in expression vectors. This peptide can be expressed and detected with the protein of interest as an amino-terminal or carboxy-terminal fusion. N-terminal FLAG vectors provide an Ek cleavage site for removal of the fusion tag. The FLAG peptide is likely to be located on the surface of a fusion protein because of its hydrophilic nature. As a result, the FLAG peptide is more likely to be accessible to antibodies. A FLAG-tag can be used in many different assays that require recognition by an antibody, such as western blotting, immunocytochemistry, immunoprecipitation, flow cytometry, protein purification, and in the study of protein-protein interactions, cell ultrastructure, and protein localization and so on.