Molecular biology

VIRION

Non enveloped, icosahedral with a T=3 symmetry, about 30 nm in diameter.

GENOME

Monopartite, linear ssRNA(+) genome of 8.5-10.2 kb, with a VPg bound at the 5’-terminus and a 3’-polyA tract. Contains two nonoverlapping open reading frames, ORF1 and ORF2, that encode the nonstructural and structural proteins, respectively.

GENE EXPRESSION

The virion RNA is infectious and serves as both genome and mRNA. The genome encodes two polyproteins from ORF1 and ORF2, the first of which encodes the non-structural proteins involved in replication, while the second, consists of three (or more) capsid proteins. Each ORF is preceded by one internal ribosome entry site (IRES) located at the 5’ end and in the middle of the mRNA.

REPLICATION

1. Virus penetrates into the cell.
2. Uncoating, and release of the viral genomic RNA into the cytoplasm.
3. Expression of the RNA1 polyprotein products that promote the replication of genomic RNAs in the cytoplasm.
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 the RNA2 polyprotein (structural proteins).
7. virus release (or cell-cell spread of viral RNAs?).