The structure of a cypovirus and the functional organization of dsRNA viruses

Cytoplasmic polyhedrosis virus (CPV) is unique among the double-stranded RN A viruses of the family Reoviridae in having a single capsid layer. Analysi s by cryo-electron microscopy allows comparison of the single shelled CPV a nd orthoreovirus with the high resolution crystal structure of the inner sh ell of the bluetongue virus (BTV) core. This suggests that the novel arrang ement identified in BTV, of 120 protein subunits in a so-called 'T=2' organ ization, is a characteristic of the Reoviridae and allows us to delineate s tructural similarities and differences between two subgroups of the family - the turreted and the smooth-core viruses. This in turn suggests a coheren t picture of the structural organization of many dsRNA viruses.