Neil S. Millar

Nucleotide Sequence of the Fusion and Haemagglutinin-Neuraminidase Glycoprotein Genes of Newcastle Disease Virus, Strain Ulster: Molecular Basis for Variations in Pathogenicity between Strains

The nucleotide sequences of the fusion (F) and haemagglutinin-neuraminidase (HN) glycoprotein genes of the extremely avirulent Newcastle disease virus (NDV) strain Ulster have been determined by sequencing cDNA clones derived from viral genomic RNA. Open reading frames, assumed to encode the F0 and HN0 glycoprotein precursors, were 553 and 616 amino acids long, respectively. Comparisons of the two glycoprotein sequences with those of more virulent NDV strains suggested an explanation for the molecular basis of the wide-ranging differences in virulence observed between strains of NDV. The open reading frame corresponding to the Ulster HN glycoprotein extended beyond the C terminus of more virulent strains. This C-terminal extension was assumed to be responsible for the origin of the HN precursor (HN0) found in strain Ulster and other extremely avirulent strains of NDV. There were fewer basic amino acids at the cleavage site of F0 in strain Ulster than are present in more virulent strains, which may be responsible for the absence of cleavage and activation of F0 from this strain in many host cells. In more virulent strains of NDV, as well as in other paramyxoviruses, a phenylalanine residue occurs at the N terminus of the F1 cleavage fragment. The occurrence of a leucine residue at this position in strain Ulster may be partly responsible for the lack of virulence of this strain.

Nucleotide Sequence of the Gene Encoding the Fusion Glycoprotein of Newcastle Disease Virus

The nucleotide sequence of the gene encoding the fusion (F) glycoprotein of the Beaudette C strain of Newcastle disease virus (NDV) has been determined from cDNA clones obtained from virion RNA. The gene is 1792 nucleotides long, including mRNA start and polyadenylation signals typical of paramyxoviruses. The single open reading frame encodes a polypeptide of 553 amino acids, with a predicted molecular weight of 59042. The F polypeptide has three regions of high hydrophobicity: an N-terminal signal peptide, the N terminus of F1 (known from protein sequencing) and a C-terminal membrane-spanning region by which the F glycoprotein is anchored to the membrane. The cleavage site of F0 is located in a highly basic region of the F polypeptide. Five potential asparagine-linked glycosylation sites are present in the amino acid sequence, of which one is in F2 and the others in F1. Comparison of the NDV F amino acid sequence to those from other paramyxoviruses reveals homology to Sendai virus, simian virus 5 and human respiratory syncytial virus. There is also limited homology between the N terminus of F1 of NDV and the N termini of HA2 of influenza viruses. Post-translational modifications of the NDV F polypeptide are discussed in the light of information provided by the amino acid sequence.

Location of a Neutralizing Epitope for the Haemagglutinin-Neuraminidase Glycoprotein of Newcastle Disease Virus

The binding site of a monoclonal antibody to the haemagglutinin-neuraminidase (HN) polypeptide of Newcastle disease virus (NDV) has been located. Complementary DNA or synthetic oligonucleotides corresponding to portions of the HN gene were cloned into the Escherichia coli vector pUC19 and fragments of the HN protein were thereby fused to the alpha-peptide of beta-galactosidase. Western blot analysis of E. coli lysates containing expressed fragments of the HN cDNA or synthetic oligonucleotides identified an antibody-binding peptide (Asp-Glu-Gln-Asp-Tyr-Gln-Ile-Arg; amino acid residues 346 to 353). Nucleotide sequence analysis of an antibody-resistant mutant of NDV revealed a Glu (wild-type) to Lys (mutant) substitution within the above sequence. The methods described could be useful for the location of continuous epitopes of other polypeptides.