Nucleotide and deduced amino acid sequence of the influenza neuraminidase genes of two equine serotypes.

Equine influenza is caused by two serotypes of type A influenza virus, EIV-A1 and EIV-A2. The complete nucleotide sequence of the neuraminidase (NA) genes of both the A1 (N7 subtype) and A2 (N8 subtype) serotype has been determined following cloning of full-length viral NA cDNAs into pBR322. Analysis of the deduced amino acid sequences reveals that the N7 and N8 genes share expected extensive homologies with the previously sequenced N1, N2, and N9 NA subtypes. These homologies include conservation of basic NA gene and protein structure, cysteine residues, potential glycosylation sites, and residues known to reside in the enzyme active site of the NA molecule. Additionally, the N1 and N8 molecules and the N7 and N9 molecules are more related by total amino acid homology than any other combination of two subtypes. The area of homology in both cases is particularly strong in the region of residues 100-205, an area roughly corresponding to the amino terminal one-third of the "head" of the NA protein.