Figure 1. Recovery and identification of recombinant viruses.

(A) Alteration of the length of the HN C-terminus by site-directed mutagenesis. “·”, stop codon; and amino acids at the carboxy terminus of the HN protein are boxed. The two recombinant viruses that could not be successfully recovered are indicated with black triangles. (B) Western blot analysis for HN proteins of recombinant viruses using polyclonal antibody raised against the NDV SG10 strain. (C) The effect of protease treatment on the extended HN mutants. Western blot analysis of HN proteins in Vero cells infected with extended HN mutants processed in the presence and absence of trypsin. Mock infection served as negative control and the V4 strain was used as positive control.