Molecular cloning and analysis of the N5 neuraminidase subtype from an avian influenza virus

The neuraminidase (NA) gene from the prototype N5 influenza virus, A/Shearwater/Australia/72, has been cloned and completely sequenced. An open reading frame of 1404 bp (468 amino acids) is flanked by 20-bp 5'- and 31-bp 3'-untranslated regions. The deduced amino acid sequence of the N5 gene was compared with sequences from N2, N1, N7, N8, and N9 subtypes. One hundred thirteen amino acid residues (24%) are completely conserved across subtypes and include active site residues, cysteines, potential glycosylation sites, and certain glycines which suggests that these subtypes share a common ancestor and adopt the same 3-D conformation. Three groups can be assigned from amino acid homologies: (i) N5, N8, N1; (ii) N7, N9; and (iii) N2 where the percentage identity within groups is 55-68% and between groups is 40-46%, the N5-N8 pair bearing the closest identity (68%). Phylogenetic analysis suggests that these groups diverged concurrently.