Labyrnavirus

VIRION

Non-enveloped, spherical, about 25 nm in diameter, T=pseudo3 icosahedral capsid surrounding the naked RNA genome. The capsid consists of a densely-packed icosahedral arrangement of 60 protomers, each consisting of 3 polypeptides.

GENOME

Monopartite, linear ssRNA(+) genome of 9 kb, polyadenylated, lacking a cap structure, has three open reading frames. ORF-1 codes for the replicases polyprotein, ORF-2 codes for the 3 structural proteins polyprotein abd ORF-3 overlaps ORF-2. The three ORFs are flanked by a 5’-UTR and a 3’-UTR. Sub-genomic RNAs are probably synthesized to translate ORF-2 and ORF-3.

GENE EXPRESSION

The virion RNA is infectious and serves as both the genome and viral messenger RNA.

REPLICATION

CYTOPLASMIC

  1. Attachement of the virus to host receptors mediates virus internalization.
  2. The viral RNA is translated into a processed polyprotein.
  3. Replication occurs in viral factories made of membrane vesicles derived from the ER. A dsRNA genome is synthesized from the genomic ssRNA(+).
  4. The dsRNA genome is transcribed/replicated thereby providing viral mRNAs/new ssRNA(+) genomes.
  5. New genomic RNA is believed to be packaged into preassembled procapsids.
  6. Virions accumulate in the host cytoplasm forming a crystalline array.
  7. Cell lysis and virus release.