title: Virulence-affecting amino acid changes in the PA protein of H7N9 influenza A viruses.
abstract: Novel avian-origin influenza A(H7N9) viruses were first reported to infect humans in March 2013. To date, 143 human cases, including 45 deaths, have been recorded. By using sequence comparisons and phylogenetic and ancestral inference analyses, we identified several distinct amino acids in the A(H7N9) polymerase PA protein, some of which may be mammalian adapting. Mutant viruses possessing some of these amino acid changes, singly or in combination, were assessed for their polymerase activities and growth kinetics in mammalian and avian cells and for their virulence in mice. We identified several mutants that were slightly more virulent in mice than the wild-type A(H7N9) virus, A/Anhui/1/2013. These mutants also exhibited increased polymerase activity in human cells but not in avian cells. Our findings indicate that the PA protein of A(H7N9) viruses has several amino acid substitutions that are attenuating in mammals.
  
  
  OBJECTIVE
  Novel avian-origin influenza A(H7N9) viruses emerged in the spring of 2013. By using computational analyses of A(H7N9) viral sequences, we identified several amino acid changes in the polymerase PA protein, which we then assessed for their effects on viral replication in cultured cells and mice. We found that the PA proteins of A(H7N9) viruses possess several amino acid substitutions that cause attenuation in mammals.
authors.affiliation: Division of Virology, Department of Microbiology and Immunology, Institute of Medical Science, University of Tokyo, Tokyo, Japan.
authors.forename: Seiya
authors.initials: S
authors.lastname: Yamayoshi
authors.forename: Shinya
authors.initials: S
authors.lastname: Yamada
authors.forename: Satoshi
authors.initials: S
authors.lastname: Fukuyama
authors.forename: Shin
authors.initials: S
authors.lastname: Murakami
authors.forename: Dongming
authors.initials: D
authors.lastname: Zhao
authors.forename: Ryuta
authors.initials: R
authors.lastname: Uraki
authors.forename: Tokiko
authors.initials: T
authors.lastname: Watanabe
authors.forename: Yuriko
authors.initials: Y
authors.lastname: Tomita
authors.forename: Catherine
authors.initials: C
authors.lastname: Macken
authors.forename: Gabriele
authors.initials: G
authors.lastname: Neumann
authors.forename: Yoshihiro
authors.initials: Y
authors.lastname: Kawaoka
mesh_terms: D019943:Amino Acid Substitution; D000818:Animals; D002645:Chickens; D004372:Ducks; D005260:Female; D006801:Humans; D064766:Influenza A Virus, H7N9 Subtype / Q000145:classification / Q000201:enzymology* / Q000235:genetics / Q000472:pathogenicity*; D009980:Influenza A virus / Q000145:classification / Q000235:genetics / Q000378:metabolism; D005585:Influenza in Birds / Q000821:virology*; D007251:Influenza, Human / Q000821:virology*; D051379:Mice; D008807:Mice, Inbred BALB C; D010802:Phylogeny; D011201:Poultry Diseases / Q000821:virology*; D012324:RNA-Dependent RNA Polymerase / Q000235:genetics* / Q000378:metabolism; D014764:Viral Proteins / Q000235:genetics* / Q000378:metabolism; D014774:Virulence
chemical_list: C061290:PA protein, influenza viruses; D014764:Viral Proteins; D012324:RNA-Dependent RNA Polymerase