A SINGLE AMINO-ACID SUBSTITUTION AT N-TERMINAL REGION OF COAT PROTEINOF TURNIP MOSAIC-VIRUS ALTERS ANTIGENICITY AND APHID TRANSMISSIBILITY

The antigenic activity of the N-terminal region of coat protein of tur nip mosaic virus (TuMV) aphid transmissible strain 1 and non-transmiss ible strain 31 was examined by using a panel of monoclonal antibodies (MAbs) raised against the two virus strains as well as antisera raised against several synthetic peptides from the N-terminal region of the protein. The reactivity of these antibodies was tested in ELISA and in a biosensor system (BIAcore Pharmacia) using virus particles, dissoci ated coat protein and synthetic peptides as antigens. Substitution of a single amino acid at position 8 in the coat protein of TuMV strain 1 abolished any cross-reactivity between MAbs to strain 1 and the subst ituted peptide (strain 31) in ELISA although some cross-reactivity was apparent in BIAcore inhibition experiments. In reciprocal tests with MAbs to strain 31 no cross-reactivity with the heterologous peptide wa s detected in either type of assay. The amino acid residue present at position 8 appears to play a critical role in the binding capacity of MAbs specific for the N-terminal region of TuMV. Antiserum to a synthe tic peptide corresponding to residues 1-14 of the protein of TuMV stra in 1 was found to react strongly with dissociated coat protein and int act virus particles and was able to inhibit the aphid transmission of the virus. Antiserum to the corresponding peptide of strain 31 did not have this capacity.