Molecular biology

VIRION

Non-enveloped, spherical, about 32-34 nm in diameter. The RNA genome is enclosed within a capsid that is composed of 60 capsid proteins, assembled into a T=1 icosahedral particle.

GENOME

Monopartite, linear, single-stranded, positive-sense RNA genome of 7.2 kb. The 5’ end is capped and the 3’ terminus is polyadenylated. Their is no VPg at the 5’-terminus of the genome. The genome consists of three partially overlapping ORFs.

GENE EXPRESSION

The virion RNA is infectious and serves as both the genome and viral messenger RNA. ORF 1 encodes the nonstructural proteins, it is not clear wether this polyprotein is cleaved or not; ORF 2 encodes the capsid protein; ORF 3 encodes a small immunogenic protein. ORF2 and ORF3 are encoded by a bicistronic subgenomic RNA.

REPLICATION

1. Virus attaches to host receptors and is internalized.
2. Uncoating, and release of the viral genomic RNA into the cytoplasm.
3. The viral RNA is 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 two other messenger RNAs, a 3.7 kb subgenomic one and a 2.0 kb coterminal one.
7. Virus release.