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

Linear, ssRNA(+) genome of 4.1 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. The genomic RNA two 5’-proximal ORFs are directly translated to produce the viral constituents of the replicase complex. The downstream genes 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

1. Virus penetrates into the host cell.
2. Uncoating, and release of the viral genomic RNA into the cytoplasm.
3. The viral RNA is translated to produce the two proteins necessary for RNA synthesis (replication and transcription).
4. A negative-sense complementary ssRNA is synthesized using the genomic RNA as a template.
5. New genomic RNA is synthesized using the negative-sense RNA as a template.
6. 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.
7. Formation of new virus particles.