Molecular evolution of hemagglutinin genes of H1N1 swine and human influenza A viruses

Shigeo Sugita, Yasuyuki Yoshioka, Shigeyuki Itamura, Yumi Kanegae, Keiko Oguchi, Takashi Gojobori, Kuniaki Nerome*, Akira Oya

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

44 Scopus citations


The hemagglutinin (HA) genes of influenza type A (H1N1) viruses isolated from swine were cloned into plasmid vectors and their nucleotide sequences were determined. A phylogenetic tree for the HA genes of swine and human influenza viruses was constructed by the neighbor-joining method. It showed that the divergence between swine and human HA genes might have occurred around 1905. The estimated rates of synonymous (silent) substitutions for swine and human influenza viruses were almost the same. For both viruses, the rate of synonymous substitution was much higher than that of nonsynonymous (amino acid altering) substitution. It is the case even for only the antigenic sites of the HA. This feature is consistent with the neutral theory of molecular evolution. The rate of nonsynonymous substitution for human influenza viruses was three times the rate for swine influenza viruses. In particular, nonsynonymous substitutions at antigenic sites occurred less frequently in swine than in humans. The difference in the rate of nonsynonymous substitution between swine and human influenza viruses can be explained by the different degrees of functional constraint operating on the amino acid sequence of the HA in both hosts.

Original languageEnglish (US)
Pages (from-to)16-23
Number of pages8
JournalJournal of Molecular Evolution
Issue number1
StatePublished - Jan 1 1991


  • Hemagglutinin gene
  • Influenza virus
  • Molecular evolution
  • Neutral theory
  • Swine virus

ASJC Scopus subject areas

  • Ecology, Evolution, Behavior and Systematics
  • Molecular Biology
  • Genetics


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