Molecular biology

VIRION

Enveloped, spherical, about 50 nm in diameter. Mature virions contain three virus-encoded membrane proteins (Erns, E1 and E2) in addition to the capsid protein.

GENOME

Monopartite, linear, ssRNA(+) genome of about 12 kb. The genome 3’ terminus is not polyadenylated, but terminates with a short poly-(C) tract. There is an IRES at the 5’ end that mediates translation initiation. Duplications, deletions, and other rearrangements are found in most cytopathic pestiviruses isolates.

GENE EXPRESSION

The virion RNA is infectious and serves as both the genome and viral messenger RNA. The whole genome is translated in a polyprotein, which is processed co- and post-translationally by host and viral proteases. There is a leader protease at the N-terminus of the polyprotein, upstream of the capsid protein cistron.

REPLICATION

1. Virus attaches to host receptors and is endocytosed into vesicles in the host cell.
2. Fusion of virus membrane with the vesicle membrane occurs; RNA genome is released into the cytoplasm.
3. The positive-sense genomic ssRNA is translated into a polyprotein, which is cleaved into all structural and non structural proteins.
4. Replication takes place at the surface of endoplasmic reticulum. A negative-sense complementary ssRNA is synthesized using the genomic RNA as a template.
5. New genomic RNA is synthesized using the negative-sense RNA as a template.
6. Virus assembly occurs at the endoplasmic reticulum. The virion buds at the endoplasmic reticulum, is transported to the Golgi apparatus, and then bud from the cell membrane.