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In this article we will discuss about the structure of reoviruses (explained with diagram).
Non-enveloped, icosahedral virion with a double capsid structure (e.g. rotavirus and orthoreovirus) where iuter capsid has an icosahedral T=13 symmetry, and inner capsid an icosahedral 7=2 symmetry. The outer capsid is positioned upon the virion in such a way that the capsomeres of each capsid layer coincide (Fig. 17.37).
The segments of genome are packaged into the core. The RNP (RNA + nucleoprotein) is in a helical form. The 3 polymerase polypeptides (PA, PB1 and PB2) are associated with each segment.
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The total size of dsRNA genome ranges from 18.2 to 30.5 kb. The linear dsRNA is segmented into 10 to 12 segments, the size of which ranges from 3.9 to 1 kb and each segment encodes 1-3 proteins. Thus the total 10-12 segments code for 10 to 14 proteins.
In Rotavirus there are three broad groups of segments of the genome which are designated as L (4 large segments which encode proteins designated as λ), M (3 medium sized segments which encode proteins designated as µ), and S (4 small segments which encode proteins designated as σ) (Fig. 17.38).
These segments range in size from ~3.9 kb (L) to 1 kb (S). In the particles, about 30% of RNA is in the form of small single-stranded oligonucleotides, synthesized internally by the viral polymerase. Proteins forming outer capsid, core and non-structural components of virions of Reoviruses, Orhiviruses and Rotaviruses are given in Table 17.11.
