The structure of the influenza A virus genome.

Influenza A viruses (IAVs) constitute a major threat to human health. The IAV genome consists of eight single-stranded viral RNA segments contained in separate viral ribonucleoprotein (vRNP) complexes that are packaged together into a single virus particle. The structure of viral RNA is believed to play a role in assembling the different vRNPs into budding virions and in directing reassortment between IAVs. Reassortment between established human IAVs and IAVs harboured in the animal reservoir can lead to the emergence of pandemic influenza strains to which there is little pre-existing immunity in the human population. While previous studies have revealed the overall organization of the proteins within vRNPs, characterization of viral RNA structure using conventional structural methods is hampered by limited resolution and an inability to resolve dynamic components. Here, we employ multiple high-throughput sequencing approaches to generate a global high-resolution structure of the IAV genome. We show that different IAV genome segments acquire distinct RNA conformations and form both intra- and intersegment RNA interactions inside influenza virions. We use our detailed map of IAV genome structure to provide direct evidence for how intersegment RNA interactions drive vRNP cosegregation during reassortment between different IAV strains. The work presented here is a roadmap both for the development of improved vaccine strains and for the creation of a framework to 'risk assess' reassortment potential to better predict the emergence of new pandemic influenza strains.