Deduced amino acid sequences at the fusion protein cleavage site of Newcastle disease viruses showing variation in antigenicity and pathogenicity.

The amino acid sequence at the F2/F1 cleavage site of the F0 fusion protein of 17 strains of Newcastle disease virus (NDV) was deduced from sequencing a 32 nucleotide area of the genome by reverse transcription and polymerase chain reaction (PCR) techniques. With the addition of sequences at the same area previously published for 9 other viruses comparisons were made of a total of 26 NDV strains and isolates (11 of low virulence, 15 of high virulence or mesogenic) covering ten antigenic groups determined by reactions with monoclonal antibodies. All the virulent viruses and the mesogenic strain Komarov showed the amino acid sequence 112R/K-R-Q-K/R-R116 for the C-terminus of the F2 protein and phenylalanine (F) at the N-terminus of the F1 protein, residue 117. The mesogenic isolate of the antigenic variant NDV responsible for the recent panzootic in racing pigeons, often termed "pigeon paramyxovirus type 1", examined in this study had the sequence 112G-R-Q-K-R-F117. The deduced amino acid sequence in the corresponding region of all viruses of low virulence was 112G/E-K/R-Q-G/E-R-L117. The virulent virus, PMV-1/chicken/Ireland/34/90 (34/90), which had a close antigenic relationship to a group of avirulent viruses, three of which were examined in the present study as representatives of the monoclonal antibody group H, showed between 4-6 nucleotide differences from these viruses in the 32 nucleotide region studied. These resulted in differences in the deduced amino acid sequence at residue 112 E-->K, 115 E-->K and 117-->F, giving 34/90 a typical virulent virus motif at the cleavage site. Despite the extremely small portion of the genome studied there were several areas which appeared characteristic for 34/90 and the three group H viruses of low virulence, which suggests that they may have arisen from the same gene pool.