Members of the Reoviridae family are non-enveloped viruses
containing genomes of 10-12 segments of double-stranded (ds) RNA
(Fig. 1). This family includes mammalian orthoreoviruses
(reoviruses), orbiviruses, and rotaviruses. Rotaviruses are the
most common cause of severe diarrheal illness in children,
causing over 50,000 hospitalizations in the U.S. and over
600,000 deaths worldwide each year. In contrast, reoviruses
infect many mammalian species, including humans, but are rarely
associated with disease. Accordingly, they serve as a useful
model for studies of virus replication, virus-cell interactions,
and viral pathogenesis. Like other members of the Reoviridae,
reovirus particles are formed from concentric protein shells.
Two such shells exist for reoviruses, termed outer capsid and
core. For reoviruses, the viral proteins are designated with a
Greek letter corresponding to the size of the encoding genome
segment: sigma (σ) for proteins encoded by small (S) genome
segments, mu (μ) by medium (M) segments,