Naturally occurring PA^E206K point mutation in 2009 H1N1 pandemic influenza viruses impairs viral replication at high temperatures

The emergence of influenza virus A pandemic H1N1 in April 2009 marked the first pandemic of the 21st century. In this study, we observed significant differences in the polymerase activities of two clinical 2009 H1N1 influenza A virus isolates from Chinese and Japanese patients. Sequence comparison of the three main protein subunits (PB2, PB1, and PA) of the viral RNA -dependent RNA polymerase complex and subsequent mutational analysis revealed that a single amino acid substitution (E206K) was responsible for the observed impaired replication phenotype. Further in vitro experiments showed that presence of PAE206K decreased the replication of influenza A/ WSN/33 virus in mammalian cells and a reduction in the virus's pathogenicity in vivo. Mechanistic studies revealed that PAE206K is a temperature -sensitive mutant associated with the inability to transport PB1-PA complex to the nucleus at high temperature (39.5 degrees C). Hence, this naturally occurring variant in the PA protein represents an ideal candidate mutation for the development of live attenuated influenza vaccines.