VIRION

Non enveloped, capsid with T=3 icosahedral symmetry, 35-40 nm in diameter.

GENOME

Segmented linear dsRNA genome: 2 segments encode for a total of 3 to 4 proteins. Segments size range from 1.7 to 2.5 kb. Genome total size is about 4 kb.

GENE EXPRESSION

Genomic segment 1 encodes for a polyprotein (ORF1) that self-cleaves to yield the mature coat protein and a large peptide. Also encodes another protein (ORF2).
Genomic segment 2 encodes for the RNA-dependent RNA polymerase.

REPLICATION

CYTOPLASMIC

1. Virus penetrates into the cytoplasm.
2. 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.
3. (+)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.
4. Mature virions are released by budding.