DYKDDDDK Tag Synthetic Peptide. DYKDDDDK Tag (FLAG-tag, FLAG octapeptide) is a polypeptide protein tag that can be added to a protein using recombinant DNA technology. The FLAG tag structure has been optimized for compatibility with the proteins it is attached to, in that it is more hydrophilic than other common epitope tags and therefore less likely to denature or inactivate proteins to which it is appended. 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. Examples are cellular localization studies by immunofluorescence or detection by SDS