Molecular biology

VIRION

Non-enveloped, icosahedral with T=3 symmetry, about 27-40 nm in diameter. The capsid is composed of 180 capsid proteins.

GENOME

Monopartite, linear, single-stranded, positive-sense RNA genome of 7.3 to 8.3 kb. At 5’-terminus a virus protein (VPg)is covalently linked to genome, whereas 3’-terminus is polyadenylated.

GENE EXPRESSION

The virion RNA is infectious and serves as both the genome and viral messenger RNA. The genome encodes a polyprotein (ORF1). Cleavage of ORF1 polyprotein by the virus-encoded 3C-like cysteine proteinase yields the mature nonstructural proteins. ORF2 encodes for a putative VP2 minor structural protein which is translated by ribosomal re-initiation.

REPLICATION

1. Virus attaches to host receptors and is internalized.
2. Uncoating, and release of the viral genomic RNA into the cytoplasm.
3. VPg is removed from the viral RNA, which is then translated into a processed ORF1 polyprotein to yield the mature non-structural proteins involved in RNA transcription.
4. Negative-sense complementary ssRNAs are synthesized using the genomic RNAs as a templates.
5. New genomic RNAs are synthesized using the negative-sense RNAs as templates.
6. Expression of sgRNA yields the basic protein (and capsid protein).
7. Assembly and release of new virions.