Orbivirus structure and assembly.

Orbiviruses (Reoviridae family) are complex nonenveloped RNA viruses with seven structural proteins and a RNA genome consisting of 10 variously sized double-stranded RNA segments. Significant advances in orbivirus research have been made in recent years through the use of gene manipulation techniques coupled with the baculovirus expression system. Several orbivirus proteins have yielded to crystallization and X-ray crystallographic structure determination and, when combined with the three-dimensional image reconstruction of virion particles and cores obtained by cryoelectron microscopy, considerable insight has been gained into the intricate organization and topography of the individual viral components. Formal identification of the sites of interaction has been obtained through protein-protein interaction studies on the components of the virion particle, including those that are involved in capsid assembly. Finally, a beginning of the understanding of the sequence of assembly events has also been obtained.