NUCLEOCAPSID AND GLYCOPROTEIN ORGANIZATION IN AN ENVELOPED VIRUS

Alphaviruses are a group of icosahedral, positive-strand RNA, envelope d viruses. The membrane bilayer, which surrounds the similar to 400 An gstrom diameter nucleocapsid, is penetrated by 80 spikes arranged in a T = 4 lattice. Each spike is a trimer of heterodimers consisting of g lycoproteins E1 and E2. Cryoelectron microscopy and image reconstructi on of Ross River virus showed that the T = 4 quaternary structure of t he nucleocapsid consists of pentamer and hexamer clusters of the capsi d protein, but not dimers, as have been observed in several crystallog raphic studies. The E1-E2 heterodimers form one-to-one associations wi th the nucleocapsid monomers across the lipid bilayer. Knowledge of th e atomic structure of the capsid protein and our reconstruction allows us to identify capsid-protein residues that interact with the RNA, th e glycoproteins, and adjacent capsid-proteins.