The T7 tag is an epitope tag composed of an 11-residue peptide encoded from the leader sequence of the T7 bacteriophage gene10. This gene encodes a T7 major capsid protein whose function is not clear. The T7 tag has been used extensively as a general epitope tag in many expression vectors including the pET system that is based on T7 RNA polymerase expression systems. This antibody recognizes the T7-tag fused to either the amino- or carboxy-terminus of targeted proteins.