Tissue polypeptide specific antigen (TPS) detects a specific epitope structure on human cytokeratin.

A TPS-reactive protein fragment from a human colon adenocarcinoma cell line was purified to electrophoretic homogeneity. N-terminal sequence analysis of the purified 13 kDa protein fragment demonstrated that the component was a fragment of human cytokeratin 18. The M3 monoclonal antibody (detector antibody in the TPS assay) was applied for screening of an expression library. The M3-reactive phage clones were subcloned and PCR amplified. DNA -sequence analysis revealed it to contain a nucleotide fragment corresponding to human cytokeratin 18. Smaller fragment, engineered by PCR and expressed as fusion proteins, demonstrated that the M3 epitope is localized to human cytokeratin 18, amino acid residues 322-340.