Molecular biology
VIRION
Non enveloped, icosahedral virion with a double capsid structure, about 70 nm in diameter. Pentameric turrets (VP2) sit on the outside of the innermost capsid (VP3). Each turret is surrounded by five peripheral trimers (VP9) and each trimer binds to three clamp proteins (VP4B). The outer incomplete 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 1162 to 3849 bp. Genome total size is about 26 kb (RRSV).
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.