Structure resolution of the trimeric RNA-dependent RNA polymerase of influenza viruses: impact on our understanding of polymerase interactions with host and viral factors.

Influenza viruses are segmented negative-sense RNA viruses whose RNA dependant RNA polymerase (RdRp) multiple activities are central for the viral life cycle. The RdRp is composed of three subunits, PB1, PB2 and PA. It binds to the extremities of each vRNA segments encapsidated with multiple copies of the Nucleoprotein (NP), altogether constituting the viral ribonucleoproteins (vRNPs). The RdRp performs both vRNA transcription and replication in the context of vRNP in the nuclei of infected cells. The temporal regulation of RdRp-associated activities is essential for the successful completion of the virus life cycle, but its understanding has been limited by the lack of structural information about the polymerase complex. The atomic-resolution of polymerase complexes from influenza virus type A, type B and type C came out in the past two years. We compile here the data provided by the near-concomitant resolution of several influenza polymerase crystal structures. We will highlight how structural information can contribute to our understanding of the interactions between the RdRp and viral or host factors.