3-DIMENSIONAL VISUALIZATION OF THE ROTAVIRUS HEMAGGLUTININ STRUCTURE

Three-dimensional structures of a native simian and reassortant rotavi rus have been determined by electron cryomicroscopy and computer image processing. The structural features of the native virus confirm that the hemagglutinin spike is a dimer of VP4, substantiated by in vivo ra diolabeling studies. Exchange of native VP4 with a bovine strain equiv alent results in a poorly infectious reassortant. No VP4 spikes are de tected in the three-dimensional reconstruction of the reassortant. The difference map between the two structures reveals a novel large globu lar domain of VP4 buried within the virion that interacts extensively with the intermediate shell protein, VP6. Our results suggest that ass embly of VP4 precedes that of VP7, the major outer shell protein, and that VP4 may play an important role in the receptor recognition and bu dding process through the rough endoplasmic reticulum during virus mat uration.