Molecular characterization of coat protein genes of serologically distinct isolates of potato virus Y necrotic strain

The coat protein (CP) genes of two potato virus Y necrotic isolates (N27 and a mutant strain N27-92), which differed in their reactivity to a monoclonal antibody (mab), were characterized. Both isolates could be detected by mab 4E7, but mab VN295.5 selectively reacted to N27 and not to N27-92. The CP genes of both isolates coded for 267 amino acids with ~99.0% identity at both the nucleotide and the amino acid levels. Nucleotide sequence comparison indicated five substitutions in N27-92 compared with N27. Three of these changes resulted in substitution of amino acids. Two transitions (A→G) in N27-92 changed threonine to alanine and lysine to arginine at positions 7 and 55, respectively, whereas a A→T transversion changed asparagine to isoleucine at position 27. The surface probability curves of both the isolates could almost be superimposed, except at amino acid positions 7 and 27. Since amino acid substitution at position 55 is conservative, changes from polar to hydrophobic amino acids (threonine→alanine and asparagine→isoleucine) at positions 7 and 27 might have changed the epitope(s) of N27-92, abolishing its detection by mab VN295.5.