Sequence of the influenza A/Udorn/72 (H3N2) virus neuraminidase gene as determined from cloned full-length DNA

Abstract

A complete nucleotide sequence was determined from cloned full-length DNA of the influenza A/Udorn/72 (H3N2) neuraminidase gene. The neuraminidase DNA has a total length of 1466 bases, excluding G-C linker residues. The cloned segment retained the common sequences known to be present at the 3′ and 5′ termini of virion RNA. Also present was a nonviral oligonucleotide nine bases long at the 5′(+) end of the DNA which represents cellular sequences acquired during influenza mRNA synthesis. The sense strand of the DNA contained a single open-reading frame coding for 469 amino acids. A possible polyadenylation site was noted downstream from the termination codon. No mammalian gene splice sequences and no alternate open-reading frame were present. The deduced amino acid sequence displayed the features of other neuraminidase genes, including the conservation of a sequence of 12 amino acids at the NH 2 terminus and the presence of a hydrophobic region from amino acid positions 7 to 34. The data were consistent with the hypothesis that this hydrophobic region of the surface glycoprotein represents the site for membrane insertion. When compared to the complete nucleotide and amino acid sequences of the influenza A/PR/8/34 (H1N1) neuraminidase, the N2 sequence revealed conservation of the positions of cysteine residues and potential glycosylation sites. Regions of homology were detected between N1 and N2 amino acid sequences, if cysteine residues of the two polypeptides were aligned. Nucleotide sequence homology between N1 and N2 was evident to a lesser degree. The data suggest that the N2 gene sequence differs from that of the N1 gene by numerous point mutations, as well as by insertion/deletion, and that the antigenic “shift” in the human neuraminidase antigenic subtype in 1957 is most likely to have occurred by replacement of the human N1 gene with one from the animal reservoir of influenza A viruses through gene reassortment.