Mesoniviridae

VIRION

Enveloped, spherical, about 60-80 nm in diameter.

GENOME

Monopartite, linear ssRNA(+) genome of about 20 kb in size.

GENE EXPRESSION

Genomic RNA encodes for ORF1a. ORF1b is translated by ribosomal frameshifting. Resulting proteins 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. Each RNA (genomic and subgenomic) is translated to yield only the protein encoded by the 5’-most ORF except for ORF2b which is possibly expressed through leaky scanning.

REPLICATION

CYTOPLASMIC

  1. Attachement to host receptors mediates 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 proteolytic cleavage of the replicase polyprotein.
  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 budding at membranes of the endoplasmic reticulum (ER), the intermediate compartments, and/or the Golgi complex.
  8. Release of new virions.