The TAP tag is an epitope attached to fusion proteins and is used for Tandem affinity purification (TAP). The C-terminal TAP tag consists of a calmodulin binding peptide (CBP) domain followed a TEV cleavage site, and then two IgG binding domains of the Staphylococcus aureus protein A (ProtA). This allows for the two-step affinity purification involving binding to IgG, partial cleavage of the tag, and then binding to calmodulin. The N-terminal TAP tag consists of ProtA, TEV, CBP, and an additional EK cleavage site. Antibodies for the TAP tag may help in additional investigations of TAP-tagged fusion proteins.