Sequence Analysis of the Haemagglutinin Genes of Ten H9N2 Subtype Avian Influenza Viruses

In order to explore the genetic mutations of the H9N2 subtype avian influenza viruses isolated in China,the complete HA segments of the ten H9N2 subtype avian influenza viruses were amplified by PCR and the sequences were analyzed on homology and heredity evolution.The results showed that the amino acid motif of cleavage sites for all the ten viruses in the HA genes were RSSR↓GLF,which was consistent with the characterization of the low pathogenic avian influenza virus.7 to 9 potential glycosylation sites were found in the HA genes and 4 mutations were found in the antigen epitope region of the HA genes of the viruses.The receptor binding sites were relatively conservative except that of 198 site and the leucine at the amino acid position 234 in the HA genes of six isolates indicated the potential of binding with SAα,2-6 receptor of mammals.The results indicated that the HA genes of the 10 viruses and the vaccine strains displayed nucleotide homologies ranging from 90.4% to 99.2% and amino acid homologies ranging from 92.2% to 98.7%,respectively.They belonged to a branch of the A/duck/Hong Kong/Y280/97 in the phylogenetic tree.The SPF chickens infected respectively by BJ15 and NJ17 isolates shed more virus and last for a longer time.The new occurring potential glycoprotein site NGT in the HA protein of BJ15 and NJ17 isolates might cause the enhancing pathogenicity.