Molecular biology

VIRION

Quasi-spherical, 26 nm in diameter, to bacilliform, 37, 43, 48 and 55 nm long and 18 nm wide, with an icosahedral T=1 symmetry. Three genomic and one subgenomic segments are encapsidated in distinct particles, resulting in several different types of virion.

GENOME

Segmented, tripartite linear ssRNA(+) genome composed of RNA1, RNA2, RNA3 kb. Each genomic segment has a 3’ tRNA-like structure and a 5’cap.

GENE EXPRESSION

Genomic RNA serves as messenger RNAs. RNA1 and RNA2 encode respectively proteins 1a and 2a, both involved in genome replication and internal transcription of sgRNA4 from the minus-strand copy of RNA3. RNA3 and sgRNA4 are translated respectively into movement and capsid proteins.

REPLICATION

CYTOPLASMIC

1. Virus attaches to host receptors.
2. Uncoating, and release of the viral genomic RNA into the cytoplasm.
3. Expression of protein 1a and 2a that promote the replication of genomic RNAs.
4. Replication of viral RNA: a negative-sense complementary ssRNA is synthesized using the genomic RNA as a template.
5. New genomic RNAs are synthesized using the negative-sense RNAs as templates.Subgenomic RNA4 is transcribed from RNA3 antigenome.
6. Subgenomic RNA4 is translated producing capsid proteins.
7. Assembly of new virions.
8. Virions are released by lysis of the cell.