The Biotin Ligase Tag is described as the minimal peptide sequence that serves as a the substrate for the E. coli biotin holoenzyme synthetase, BirA. In the presence of active BirA, the biotin ligase tag (also known as the biotin acceptor peptide) becomes biotinylated, allowing for detection or purification with streptavidin. Antibodies to the biotin ligase tag recognize the epitope sequence, GLNDIFEAQKIEWH, and may serve as a useful tool in the detection of tagged proteins.