Role of the cytoplasmic tail amino acid sequences of Newcastle disease virus hemagglutinin-neuraminidase protein in virion incorporation, cell fusion, and pathogenicity.

To determine the role of amino acid sequences of the hemagglutinin-neuraminidase (HN) cytoplasmic tail in Newcastle disease virus (NDV) replication and pathogenicity, we generated recombinant NDVs with a deletion or point mutation in the N-terminal cytoplasmic tail. The first 2-amino-acid deletion in the cytoplasmic tail did not affect the biological characteristics of NDV. However, a 4-amino-acid deletion and the substitution of alanine for serine at position 6 affected cell fusion, pathogenicity, and colocalization of the HN and M proteins of NDV, indicating that these residues of the HN cytoplasmic tail are critical for its specific incorporation into virions.