VIRION
Enveloped, spherical, icosahedral, 65-70nm in diameter, capsid with a T=4 icosahedral symmetry made of 240 monomers. The envelope contains 80 trimer spikes, each spike = 3 x E1/E2 heterodimers.
GENOME
Monopartite, linear, ssRNA(+) genome of 9.7 kb. The genome is capped and polyadenylated.
GENE EXPRESSION
The virion RNA is infectious and serves as both genome and viral messenger RNA. The whole genome is translated in a non-structural polyprotein which is processed by host and viral proteases. Structural polyprotein is expressed through a subgenomic mRNA.
REPLICATION
CYTOPLASMIC
- Attachement of the viral E glycoprotein to host receptors mediates clathrin-mediated endocytosis of virus into the host cell.
- Fusion of virus membrane with host endosomal membrane. RNA genome is released into the cytoplasm.
- The positive-sense genomic ssRNA is translated into a polyprotein, which is cleaved into non-structural proteins necessary for RNA synthesis (replication and transcription).
- Replication takes place in cytoplasmic viral factories at the surface of endosomes. A dsRNA genome is synthesized from the genomic ssRNA(+).
- The dsRNA genome is transcribed/replicated thereby providing viral mRNAs/new ssRNA(+) genomes.
- Expression of the subgenomic RNA (sgRNA) gives rise to the structural proteins.
- Virus assembly occurs at the endoplasmic reticulum.
- Virions bud at the endoplasmic reticulum, are transported to the Golgi apparatus, and then exit the cell via the secretory pathway.
