Sapovirus

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.

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. Cleavage of ORF1 polyprotein by the virus-encoded 3C-like cysteine proteinase yields the mature nonstructural proteins and the capsid protein. ORF2 encodes a small structural protein VP2 which is expressed through RNA termination-reinitiation.

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.