Molecular biology
VIRION
Non enveloped, icosahedral virion with a double capsid structure, about 65-70 nm in diameter. Pentameric turrets sit on the outside of the innermost capsid. The outer capsid has an icosahedral T=13 symmetry, the inner capsid an icosahedral symmetry T=2.
GENOME
Segmented dsRNA linear genome. Contains 10 segments coding for 12 proteins. Segments size range from 1.4 to 4.5 kb. Genome total size is about 27-30 kb.
GENE EXPRESSION
The dsRNA genome is never completely uncoated, to prevent activation of antiviral state by the cell in response of dsRNA. The viral polymerase synthesizes a capped mRNA from each dsRNA segment. This capped mRNA is translocated to the cell cytoplasm where it is translated.
REPLICATION
CYTOPLASMIC
- Virus penetrates into the cytoplasm.
- Transcription of the dsRNA genome by viral polymerase occurs inside the virion, so that dsRNA is never exposed to the cytoplasm. This plus-strand transcript is used as template for translation.
- (+)RNAs are encapsidated in virion particle, inside which they are transcribed to give RNA (-) molecules with which they become base-paired to produce dsRNA genomes.
- Mature virions are released presumably following cell death and associated breakdown of host plasma membrane.