Tag:APEP is an artificial 14 amino acid residue consensus peptide (GLNDIFEAQKIEWH) that can be biotinylated efficiently in vivo by the Ecol\birA biotin ligase. The biotinylated tag can be used as an affinity tag for one-step purification, by binding to streptavidin, of the tagged protein or its complexes (PMID:10211839).