The DYKDDDDK peptide (Flag) is used as a fusion tag for immunoaffinity chromatography. The monoclonal antibody M1 binds the peptide in presence of bivalent metal cations such as Ca2+. Flag is a registered trademark of Sigma-Aldrich.H-Asp-Tyr-Lys-Asp-Asp-Asp-Asp-Lys-OH or H-DYKDDDDK-OH