Coltivirus (taxid:10911)

VIRION

Non enveloped, icosahedral virion with a triple capsid structure, about 60-80 nm in diameter. Pentameric turrets sit on the outside of the innermost capsid. The intermediate capsid has a T=13 icosahedral symmetry, the inner capsid a T=2* icosahedral symmetry.

GENOME

Segmented dsRNA linear genome. Contains 12 segments coding for 13 proteins. Segments size range from 675 to 4,350 bp and genome total size is about 29,000 bp (CTFV).

GENE EXPRESSION

The dsRNA genome is never completely uncoated, to prevent activation of antiviral state by the cell in response to dsRNA. The viral polymerase VP1 synthesizes a capped mRNA from each dsRNA segment. This capped mRNA is translocated to the cell cytoplasm where it is translated. VP9 protein is expressed via RNA suppression of termination.

ENZYMES

• RNA-dependent RNA polymerase VP1
• Cell-type capping:
  • RNA TPase
  • N7 MTase VP3
  • GTase VP3
  • 2'O MTase VP3

REPLICATION

CYTOPLASMIC

1. Attachment to host receptors probably mediates endocytosis of virus into host cell.
2. Particles are partially uncoated in endolysosomes, but not entirely, and penetrate in the cytoplasm.
3. 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.
4. Full-length plus-strand transcripts from each of the dsRNA segments are synthesized. These plus-strand transcripts are used as templates for translation.
5. Viral proteins and genomic RNAs aggregates in cytoplasmic viral factories.
6. (+)RNAs are encapsidated in a sub-viral particle, in which they are transcribed to give RNA (-) molecules with which they become base-paired to produce dsRNA genomes.
7. The capsid is assembled on the sub-viral particle.
8. Mature virions are released presumably following cell death and associated breakdown of host plasma membrane.