Sequence of the neuraminidase gene of influenza virus A/Tokyo/3/67 and previously uncharacterized monoclonal variants.

A full-length cDNA copy of the neuraminidase (NA) gene of influenza strain A/Tokyo/3/67 was cloned into the plasmid pBR322, and the nucleotide sequence of the gene was determined. In addition, the sequence changes in six variants of A/Tokyo/3/67 selected with various monoclonal antibodies (Ab) to the NA were determined by dideoxy sequencing of the vRNA. In five of the monoclonal variants, a single change occurred, resulting in an amino acid substitution at residue 344. Arginine in the parent virus changed to every amino acid possible with a single nucleotide change. In another variant, arginine at position 253 changed to serine, a change that also occurred in field strains. All variants so far sequenced that were selected by monoclonal Ab to A/Tokyo/3/67 virus changed at position 344, except one which changed at residue 368. Both of these positions are in clusters of residues that vary considerably in field strains, the clusters being 344-347 and 368-370. Analysis of the three-dimensional crystal structure of the NA of A/Tokyo/3/67 shows that these clusters are directly adjacent on the protein, and likely comprise a single antigenic site. A total of three or four antigenic sites have been proposed for the NA protein, based on antigenic mapping with monoclonal Ab [R. G. Webster, V. S. Hinshaw , and W. G. Laver (1982) Virology 117, 93-104]. Variants selected by Ab to Tokyo/67 NA all change in this single antigenic site, whereas variants selected by Ab to other strains change in other regions. It is possible that, although there may be three or four antigenic sites on the NA molecule, there may be a single, dominant antigenic site for each strain.