Molecular biology
VIRION
Non enveloped, icosahedral virion with a double capsid structure (except for cypoviruses and dinovernaviruses which have only the equivalent of the inner 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 to 12 segments coding for 10 to 14 proteins. Segments size range from 0.2 to 3.0 kb. Genome total size range from 18.2 to 30.5 kb.
GENE EXPRESSION
The dsRNA genome is never completely uncoated, to prevent activation of antiviral state by the cell in response of dsRNA. Viral polymerase synthesizes mRNA from each dsRNA segment which are translocated to the cell cytoplasm where they are translated.
Further proteins are produced by alternative initiation and protein processing.
REPLICATION
CYTOPLASMIC
- Virus attaches to host receptors and is endocytosed into vesicles in the host cell.
- Particles are partially uncoated in endolysosomes, but not entirely, and penetrates in the cytoplasm.
- Early transcription of the dsRNA genome by viral polymerase occurs inside this sub-viral particle (naked core), so that dsRNA is never exposed to the cytoplasm. Full-length plus-strand transcripts from each of the dsRNA segments are synthesized. These plus-strand transcripts are used as templates for translation.
- (+)RNAs are encapsidated in a sub-viral particle, inside which they are transcribed to give RNA (-) molecules with which they become base-paired to produce dsRNA genomes.
- The capsid is assembled on the sub-viral particle.
- Mature virions are released presumably following cell death and associated breakdown of host plasma membrane.