TABLE 3 

Amino acids at key codons in the IAV genome

HostVirus, subtype,
or location
PB2aPA-XbNAcM2d
CanineCIV-H1N1E627TruncatedH275N31
CIV-H3N2E627TruncatedH275S31
CIV-H3N8E627TruncatedH275S31
EquineEIV H7N7E627CompleteH275S31
EIV H3N8E627CompleteH275S31
SwineCswH1K627Complete/TruncatedH275S31
EAswH1E627CompleteH275N31
TRswH3E627TruncatedH275S31
PDMswH1E627TruncatedH275N31
HumanH1N1 (seasonal)K627CompleteH275 (1918–2006)S31
Y275 (2007–2009)
H1N1pdmE627TruncatedH275/Y275N31
H2N2K627CompleteH275S31
H3N2K627CompleteH275S31 (1968–2002)
N31 (2003–2017)
AvianEurasianE627CompleteH275S31/N31
North AmericanE627CompleteH275S31
  • a The E627K substitution in the PB2 polymerase protein increases replication efficiency in mammals (35).

  • b PA-X is a fusion protein that modulates host cellular immune responses (63). The protein is encoded by a +1 frameshift open reading frame (ORF), and a synonymous mutation in the PA gene produces a nonsense mutation at PA-X codon 42 (34).

  • c The H274Y substitution (H275Y N1 numbering) in the NA protein is associated with reduced susceptibility to oseltamivir antivirals (64).

  • d The S31N substitution in the M2 ion channel protein is associated with reduced susceptibility to adamantane antivirals (65).