Molecular biology
VIRION
Non enveloped, icosahedral, non-turreted virion with a double capsid structure, about 70 nm in diameter. The outer capsid has an icosahedral T=13 symmetry, the inner capsid an icosahedral symmetry T=2. Each double-layered capsid consists of 260 trimers of the major outer capsid P8 protein and 60 dimers of the inner capsid P3 protein.
GENOME
Segmented dsRNA linear genome. Contains 12 segments coding for 15 proteins. Segment 11 has two in-frame codons resulting in two ORFs. Segment 12 has two additional overlapping ORFs. Segments size range from 1066 to 4423 bp. Genome total size is about 26 kb (WTV).
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.