Nucleotide sequence analysis of the haemagglutinin-neuraminidase gene of Newcastle disease virus.

The nucleotide sequence of the haemagglutinin-neuraminidase (HN) gene of Newcastle disease virus (NDV) has been determined. The HN gene is 2031 nucleotides long, approximately 13.5% of the viral genome. The nucleotide sequence contains a single long open reading frame which would encode a protein of 577 amino acids, with a mol. wt. of 63,149. This is in good agreement with estimates of the molecular weight of the unglycosylated HN protein. Analysis of the amino acid sequence reveals six potential glycosylation sites and shows the major hydrophobic region to be close to the N terminus. This provides evidence for the N-terminal attachment of HN to the viral membrane. The hydrophilic nature of the extreme N-terminal amino acids suggests the absence of a cleaved signal sequence. Analysis of the long non-coding region at the 3' end of the mRNA encoded by the HN gene of NDV suggests a possible explanation for the origin of HN0 in extremely avirulent strains of NDV. There are regions of high homology between the deduced amino acid sequence of the NDV HN glycoprotein and the HN glycoproteins of two other paramyxoviruses, Sendai virus and simian virus 5 (SV5). An alignment of the HN amino acid sequences of these viruses shows 32% of amino acid residues are conserved between NDV and SV5, and 23% between NDV and Sendai virus. In contrast, only very limited homology is found between NDV HN and the influenza virus glycoproteins.