This invention is concerned with a peptide tag having sequence SSTSSDFRDR or GVSSTSSDFRDR derived from transactivator protein E2 of Bovine Papillomavirus type 1, and the fusion polypeptide containing said peptide tag, and the expression vector comprising the oligonucleotide sequence encoding said peptide tag. The invention relates also to the antibodies specific for the peptide tag and the methods for detecting and purifying tagged proteins.