"The processes regulating emergence of viruses into the human population involve a complex interplay between virus and host," Doudna says, "and understanding the mechanisms by which influenza viruses acquire the ability to infect multiple species is imperative to controlling future outbreaks. Transmission of the influenza virus into a new species can be influenced by mutations in any of the virus's eight genes."
The influenza polymerase consists of three proteins dubbed PB1, PB2 and PA, that work with viral RNA and nucleoprotein to transcribe and replicate the influenza genome in a host cell. Earlier work by Doudna and Mehle with avian influenza had shown that a mutation in the viral protein PB2 - whereby glutamic acid is replaced at a certain position on the amino acid chain with lysine - enables the virus to jump from birds to humans. When glutamic acid is retained in PB2, its presence suppresses the polymerase from performing in human cells.
"That's why we were surprised when we looked at the gene sequences for the current H1N1 polymerase," Mehle says. "The viruses were replicating in people yet they retained the inhibitory glutamic acid in PB2."
In their investigation, Mehle and Doudna found that the 2009 H1N1 virus has acquired the SR polymorphism in its PB2 protein that enhances polymerase activity in human cells. To confirm that the SR polymorphism was a new pathway for the virus to infect humans, they introduced the mutation into the PB2 protein of the avian influenza. As with swine influenza, the polymerase activity and viral replic
|Contact: Lynn Yarris|
DOE/Lawrence Berkeley National Laboratory