High-Resolution Structures of Tobacco Mosaic Virus Disks from Cryo-Electron Microscopy

Tobacco mosaic virus has been involved in many important developments in virology, structural biology, and biotechnology. Despite decades of study, several key aspects of the viral assembly mechanism remain unclear, particularly the structure of the coat protein disk that initiates virus assembly by interacting with the viral RNA. Here we report the first cryo-electron microscopy structures of the coat protein disk under conditions typically used for in vitro virus assembly. We identify 1-, 2-, and 3-layered disks, all of which differ significantly from previous structures obtained by X-ray crystallography. These new models lead to a revised viral assembly mechanism. We also compare coat proteins produced in bacteria and plants to better understand the effect of N-terminal acetylation.