The AU1 tag is a short six-peptide epitope consisting of the sequence DTYRYI. It originates from the major capsid protein of the bovine papillomavirus-1 (BPV-1). The tag is often attached to N- or C- termini of recombinant proteins of interest for immunological analysis. Antibodies that target the AU1 epitope may be a useful tool in the investigation of AU1-tagged proteins.