Molecular biology
VIRION
Non enveloped, icosahedral virion with a double capsid structure, about 80 nm in diameter. Pentameric turrets sit on the outside of the innermost capsid. The outer capsid a has an icosahedral T=13 symmetry, the inner capsid an icosahedral T=2 symmetry.
Virion maturation schemes
GENOME
Segmented dsRNA linear genome. Contains 10 segments: L1, L2, L3, M1, M2, M3, S1, S2, S3, S4, coding for 12-13 proteins. Segments size range from 1,189 to 3,916nt (MRV-3De). Genome total size is 23.5 Kb (MRV-3De).
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 lambda3 synthesizes a capped and non-polyadenylated monocistronic mRNA from each dsRNA segment. These capped mRNAs are translocated to the cell cytoplasm where they are translated.
REPLICATION
CYTOPLASMIC
- Virus attaches to host receptors and is endocytosed into vesicles in the host cell.
- Particles, partially uncoated in endolysosomes, but not entirely, are termed infectious subvirion particles (ISVP). They penetrate in the cytoplasm through pore formation by released viral peptides arising from the proteolytic cleavage of mu-1.
- Early transcription of the dsRNA genome by viral polymerase occurs inside this sub-viral particle (naked core), so that dsRNA is never exposed to the cytoplasm. Full-length plus-strand transcripts from each of the dsRNA segments are synthesized. These plus-strand transcripts are used as templates for translation.
- (+)RNAs are encapsidated in a sub-viral particle, inside which they are transcribed to give RNA (-) molecules with which they become base-paired to produce dsRNA genomes.
- The capsid is assembled on the sub-viral particle.
- Mature virions are released presumably following cell death and associated breakdown of host plasma membrane.