Cypovirus (taxid:10981)

VIRION

Non enveloped, icosahedral virion with a T=2* icosahedral symmetry, about 65 nm in diameter. Pentameric turrets sit on the outside of the capsid. The capsid is composed of only a single shell of protein.

GENOME

Segmented dsRNA linear genome: 10 segments encode for 10-12 proteins. Segments size range from 1 to 4.2 kb. Genome total size is about 25 kb.

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 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.
NSP5 ORF produces two proteins by ribosomal skipping.

ENZYMES

• RNA-dependent RNA polymerase [VP2]
• Cell-type capping:
  • RNA TPase
  • N7 MTase [VP4]
  • GTase [VP4]
  • 2'O MTase [VP4]

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.