The peptide sequence of the FLAG-tag from the N-terminus to the C-terminus is: DYKDDDDK (1012 Da). It can be used in conjunction with other affinity tags, for example a polyhistidine tag, HA-tag or myc-tag. It can be fused to the C-terminus or the N-terminus of a protein. Some commercially available antibodies (e.g. M1/4E11) recognize the epitope only when it is present at the N-terminus. However, other available antibodies (e.g. M2) are position-insensitive.
Protein Ark also supplies the 3X FLAG peptide, which is also a synthetic peptide of 23 amino acid residues (2862 Da). The Asp-Tyr-Lys-Xaa-Xaa-Asp motif is repeated three times in the peptide. Eight amino acids at the C-terminus make up the classic FLAG sequence (Asp-Tyr-Lys-Asp-Asp-Asp-Asp-Lys).