VIRION
Non enveloped, single-shelled T=13 icosahedral symmetry capsid of about 70 nm in diameter, composed of 260 trimers of VP2 that form spikes projecting radially from the capsid. The peptides derived from pre-VP2 C-terminal cleavages remain associated within virion. VP3 forms a ribonucleoprotein complex with the genomic RNA. Minor amounts of VP1 are also incorporated in the virion.
GENOME
Segmented linear dsRNA genome: 2 segments (A,B) encode for 5 proteins. VP1 is found in a free form and covalently attached at the 5' genomic RNA end (VPg). Segments size is about 3.2-3.5 kb. Genome total size is about 6.5 kb.
GENE EXPRESSION
Genomic segment A encodes for a structural polyprotein which is matured in cis by VP4. It also encodes an alternative ORF translated possibly by leaky scanning (VP5).
Genomic segment B encodes for VP1.
ENZYMES
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 by budding.