Molecular biology
VIRION
Non-enveloped, isometric, icosahedral, about 28-34 nm in diameter. 30 hexameric capsomers per nucleocapsid (virion composed of 180 protein subunits).
GENOME
Monopartite (except Dianthovirus which is bipartite), linear, ssRNA(+) genome of 4-5.4 kb, which lacks a cap structure and a poly(A)tail.
GENE EXPRESSION
The virion RNA is infectious and serves as both the genome and viral messenger RNA. Two 5’-proximal ORFs are directly translated to produce the viral constituents of the replicase complex. The downstream genes encoding the movement and capsid proteins are translated from subgenomic RNAs.
Cap-independent translation is mediated possibly through the interaction between a 3’-cap-independent translation element and a 5’UTR stem-loop.
REPLICATION
CYTOPLASMIC
- Virus penetrates into the host cell.
- Uncoating, and release of the viral genomic RNA into the cytoplasm.
- The viral RNA is translated to produce the two proteins necessary for RNA synthesis (replication and transcription).
- A negative-sense complementary ssRNA is synthesized using the genomic RNA as a template.
- New genomic RNA is synthesized using the negative-sense RNA as a template.
- The RdRp recognizes internal subgenomic promoters on the negative-sense RNA to transcribe the 3’co-terminal subgenomic RNAs that will generate the capsid and movement proteins.
- Formation of new virus particles.