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.
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.