Fig. 5: The structures of the tribasic HA cleavage sites and growth property of tribasic H9N2 viruses.

a The predicted RNA secondary structures of tribasic HA cleavage sites and amino acids corresponding to each codon are shown. The Quickfold program (http://unafold.rna.albany.edu/?qDINAMelt/Quickfold) and RNAfold program from the ViennaRNA Web Services (http://rna.tbi.univie.ac.at/) and the ViennaRNA package were used to predict RNA sequences of the cleavage site regions of the HA genes. b Growth curves after inoculation of each virus at a multiplicity of infection of 0.001 into MDCK cell. Each point on the curve is the mean ± standard deviation from three independent experiments. c Three-dimensional (3D) structural analysis of amino acids at the HA cleavage site. A side view of the HA trimer structure of influenza A virus based on the uncleaved H3 monomer (protein Data Bank ID 4BSE) as a template. The corresponding amino acids to a 3D structure of the HA protein containing different cleavage motifs were mapped using MacPymol (http://www.pymol.org/).