Influenza A H5N1 (Avian) Nonstructural Protein 1 (NS1)

The NS1 protein of influenza A virus (NS1A protein) is a multifunctional protein that counters cellular antiviral activities and is a virulence factor. The influenza protein NS1 is a 26,000 Dalton protein. Human messenger RNA carries a poly-A tail at the 5' end. NS1 forms a dimer that inhibits the export of poly-A containing mRNA molecules from the nucleus. This gives preference to viral RNA which is transported to the ribosome to be translated. NS1 might also inhibit splicing of pre-mRNA by binding to a stem-bulge region in U6 small nuclear RNA (snRNA). In addition, NS1 is probably able to suppress the interferon response in the virus-infected cell leading to unimpaired virus production. NS1 also binds dsRNA. The NS1 protein of the highly pathogenic avian H5N1 viruses circulating in poultry and waterfowl in Southeast Asia is currently believed to be responsible for the enhanced virulence of the strain. H5N1 NS1 is characterized by a single amino acid change at position 92. By changing the amino acid from glutamic acid to aspartic acid, researchers were able to annul the effect of the H5N1 NS1. This single amino acid change in the NS1 gene greatly increased the pathogenicity of the H5N1 influenza virus.