Molecular biology
VIRION
Non enveloped, T=3 icosahedral, 29 nm in diameter, composed of 180 coat proteins: 12 pentamers and 20 hexamers.
GENOME
Segmented, tripartite linear ssRNA(+) genome composed of RNA1, RNA2, RNA3. Each genomic segment has a 3’ tRNA-like structure and a 5’cap.
GENE EXPRESSION
Genomic RNA serves as messenger RNAs. RNA1 and RNA2 encode respectively proteins 1a and 2a, both involved in genome replication and internal transcription of sgRNA4 from the minus-strand copy of RNA3. RNA3 and sgRNA4 are translated respectively into movement and capsid proteins. ORF2b encodes a viral suppressor of RNA silencing.
REPLICATION
CYTOPLASMIC
- Virus attaches to host receptors.
- Uncoating, and release of the viral genomic RNA into the cytoplasm.
- Expression of protein 1a and 2a that promote the replication of genomic RNAs.
- Replication of viral RNA: a negative-sense complementary ssRNA is synthesized using the genomic RNA as a template.
- New genomic RNAs are synthesized using the negative-sense RNAs as templates.Subgenomic RNA4 is transcribed from RNA3 antigenome.
- Subgenomic RNA4 is translated producing capsid proteins.
- Assembly of new virions.
- Virions are released by lysis of the cell.