Kappaarterivirus (taxid:2499676)

VIRION

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Enveloped, spherical, about 45-60 nm in diameter. The virion is comprised of an isometric core of 20-30 nm surrounded by a lipid-containing envelope. The RNA genome associates with the N protein to form the nucleocapsid.

GENOME

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Monopartite, linear, ssRNA(+) genome of 12-13kb in size, capped, and polyadenylated. The leader RNA (65-89 bp) at the 5' end of the genome is also present at the end of each subgenomic RNAs.

Enzymes: EndoU ribonuclease

GENE EXPRESSION

The virion RNA is infectious and serves as both genome and viral messenger RNA. ORF1b is translated by a ribosomal frameshifting. Polyproteins pp1a and pp1ab are processed into the viral polymerase (RdRp) and other non-structural proteins involved in RNA synthesis. Structural proteins are expressed as subgenomic RNAs. The mRNA2 is bicistronic. Protein GP2 and 5a are produced by leaky scanning from the E and gp5 subgenomic mRNA respectively.

ENZYMES

REPLICATION

CYTOPLASMIC

  1. Attachement to host receptors mediates clathrin-mediated endocytosis of the virus into the host cell.
  2. Fusion of virus membrane with the endosomal membrane. ssRNA(+) genome is released into the cytoplasm.
  3. Synthesis and proteolysis of replicase polyproteins.
  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. Synthesis of structural proteins encoded by subgenomic mRNAs.
  7. assembly and ESCRT-independent budding at the membranes of endoplasmic reticulum (ER), intermediate compartments, and/or Golgi complex.
  8. Release of new virions by exocytosis.