Caliciviridae

VIRION

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Non-enveloped, capsid of about 27-40 nm in diameter, with T=3 icosahedral symmetry. The capsid is composed of 180 capsid proteins.
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GENOME

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Monopartite, linear ssRNA(+) genome of 7.3 to 8.3 kb. The 5'-terminus is linked to a VPg protein and the 3'-terminus has a poly(A) tract.

GENE EXPRESSION

The virion RNA is infectious and serves as both the genome and viral messenger RNA. The genome encodes a polyprotein (ORF1). One or two smaller ORFs are expressed from a subgenomic RNA. Cleavage of ORF1 polyprotein by the virus-encoded 3C-like cysteine proteinase yields the mature nonstructural proteins. The 3'-end terminal ORF encodes a basic protein (and the capsid protein) and is expressed through RNA termination-reinitiation.
Some Norovirus expressan alternative ORF by leaky scanning Vesiviruses are apparently unique among the Caliciviridae in that the ORF2 encodes a capsid precursor protein that is proteolytically processed by the viral proteinase to yield the mature capsid protein.

REPLICATION

CYTOPLASMIC

  1. Attachement to host receptors mediates endocytosis of the virus into the host cell.
  2. Uncoating, and release of the viral genomic RNA into the cytoplasm.
  3. VPg is removed from the viral RNA, which is then translated into a processed ORF1 polyprotein to yield the replication proteins.
  4. Replication occurs in viral factories. A dsRNA genome is synthesized from the genomic ssRNA(+).
  5. The dsRNA genome is transcribed/replicated thereby providing viral mRNAs/new ssRNA(+) genomes.
  6. Subgenomic RNA translation gives rise to the capsid protein and VP2.
  7. Assembly of new virus particles and release by cell lysis.

Host-virus interaction

Apoptosis modulation

Murine norovirus and rabbit hemorrhagic disease virus induce host cell apoptosis .

Host gene expression shutoff by virus

Noroviruses and Vesiviruses mediate host translation shutoff by cleaving PABP1 .