3-DIMENSIONAL STRUCTURE OF A MEMBRANE-CONTAINING VIRUS

The structure of Sindbis virus was determined by electron cryomicrosco py. The virion contains two icosahedral shells of viral-encoded protei ns separated by a membrane bilayer of cellular origin. The three-dimen sional structure of the ice-embedded intact Sindbis virus, reconstruct ed from electron images, unambiguously shows that proteins in both she lls are arranged with the same icosahedral lattice of triangulation nu mber T = 4. These studies also provide structural evidence of contact between the glycoprotein and the nucleocapsid protein across the membr ane bilayer. The structural organization of Sindbis virus has profound implications for the morphogenesis of the alphaviruses. The observed interactions confirm stoichiometric and specific protein associations that may be crucial for virion stability and predict a mechanism for a ssembly.