Molecular biology

VIRION

Non enveloped, spherical virion with icosahedric symmetry, about 30 nm in diameter.

GENOME

Linear ssRNA(+) genome of 8.8-9.7 kb in size. Vpg protein is covalently attached to the genomic 5’ terminus, 3’ terminus is polyadenylated. The long UTR at the 5’ end contains an internal ribosome entry site (IRES).

GENE EXPRESSION

The viral RNA is infectious and serves as both the genome and viral messenger RNA. The IRES allows direct translation of the polyprotein. The polyprotein is initially processed by the viral protease(s) into various precursor and mature proteins to yield the structural proteins, replicase, VPg, and a number of proteins that modify the host cell, ultimately leading to cell lysis.

REPLICATION

CYTOPLASMIC

1. Virus attaches to host receptors, formation of a coated vesicle.
2. Uncoating, and release of the viral genomic RNA into the cytoplasm possibly through the formation of a pore in the host cell membrane.
3. Genomic RNA is translated into a polyprotein, which is autocatalytically processed.
4. Shutoff of cellular cap-dependent translation through the cleavage of the translation initiation factor eIF4G by the leader protease.
5. Replication of viral RNA takes place on membrane vesicles derived from the ER. A negative-sense complementary ssRNA is synthesized using the genomic RNA as a template.
6. New genomic RNA synthesized using the negative-sense RNA as a template is believed to be packaged into preformed procapsids.
7. Cell lysis and virus release.