VIRION
Non-enveloped icosahedral capsid, about 50 nm in diameter. Presumably T=1 icosahedral symmetry but has not been determined.
GENOME
Segmented linear dsRNA genome: 2 segments encoding potentially for 4 proteins. Segments are about 7 kb and 9 kb.
GENE EXPRESSION
The coding strands of RNA-1 and RNA-2 contain two non-overlapping tandem ORFs. A single major capsid protein of 135 kDa is encoded by RNA-1. Translation is likely initiated by a unique internal ribosome entry site (IRES) element at the 5'-UTR.
ENZYMES
- RNA-directed RNA polymerase [RdRp]
- No capping activity [IRES]?
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, in which they are transcribed to give RNA (-) molecules with which they become base-paired to produce dsRNA genomes.
- Mature are transmitted to new cell during cell division, sporogenesis or cell fusion.