Molecular basis of influenza ribonucleoprotein complex assembly and processive RNA synthesis.

Influenza viruses replicate and transcribe their genome in the context of a conserved ribonucleoprotein (RNP) complex. By integrating cryo-electron microscopy single-particle analysis and cryo-electron tomography, we define the influenza RNP as a right-handed, antiparallel double helix with the viral RNA encapsidated in the minor groove. Individual nucleoprotein subunits are connected by a flexible tail loop that inserts into a conserved pocket in its neighbor. We visualize the viral polymerase in RNP at different functional states, revealing how it accesses the RNA template while maintaining the double-helical architecture of RNP by strand sliding. Targeting the tail loop binding interface, we identify lead compounds as potential anti-influenza inhibitors. These findings elucidate the molecular determinants underpinning influenza virus replication and highlight a promising target for antiviral development.