A host range mutant of Newcastle disease virus with an altered cleavage site for proteolytic activation of the F protein.

The primary structure of the F protein of a host range mutant of the Ulster strain of Newcastle Disease virus (NDV) has been determined by nucleotide sequence analysis and compared to that of the wild type and other NDV strains. The cleavage site of the mutant had the sequence Gly-Lys-Gln-Arg-Arg as compared to two isolated basic amino acids [Gly-Lys(Arg)-Gln-Gly-Arg] with the apathogenic strains and two pairs of basic amino acids [Arg-Arg-Gln-Lys(Arg)-Arg] with the pathogenic strains. The data indicate that the cleavability of the F protein of NDV increases with the number of arginine and lysine residues at the cleavage site and that the susceptibility of the pathogenic strains to ubiquitous host proteases depends on both pairs of basic amino acids.