https://www.fciencias.com/2017/09/21/proteina-flag-tag-molec...
FLAG-tag (também conhecido como péptido ou epítopo FLAG) é um polipéptido usado como marcador de proteínas recombinantes em técnicas de engenharia genética e manipulação de DNA. É composto por oito aminoácidos, tem um peso molecular de 1012 Dalton e a sua sequência peptídica, da região N-terminal à região C-terminal, é DYKDDDDK (em que D = ácido aspártico, Y – tirosina e K = lisina).


https://en.wikipedia.org/wiki/FLAG-tag
FLAG-tag, or FLAG octapeptide, or FLAG epitope, is a peptide protein tag that can be added to a protein using recombinant DNA technology, having the sequence DYKDDDDK (where D=aspartic acid, Y=tyrosine, and K=lysine).[1] It is one of the most specific tags[2] and it is an artificial antigen to which specific, high affinity monoclonal antibodies have been developed and hence can be used for protein purification by affinity chromatography and also can be used for locating proteins within living cells. FLAG-tag has been used to separate recombinant, overexpressed protein from wild-type protein expressed by the host organism. FLAG-tag can also be used in the isolation of protein complexes with multiple subunits, because FLAG-tag's mild purification procedure tends not to disrupt such complexes. FLAG-tag-based purification has been used to obtain proteins of sufficient purity and quality to carry out 3D structure determination by x-ray crystallography.