Molecular biology

VIRION

Enveloped, bacilliform-shaped, about 150-200 nm x 40-60 nm. Nucleocapsid have helical symmetry with diameter of 20-30nm.

GENOME

Monopartite, linear,positive sense ssRNA genome of 26 kb in size. Capped, and polyadenylated.

GENE EXPRESSION

The virion RNA is infectious and serves as both the genome and viral messenger RNA. Genomic RNA encodes for ORF1a, and ORF1b is translated by a frameshifting mechanism. Resulting proteins pp1a and pp1ab are processed into the viral polymerase (RdRp) and other non-structural proteins involved in RNA synthesis. Structural proteins are expressed as subgenomic RNAs. Each RNA (genomic and subgenomic) is translated to yield only the protein encoded by the 5’-most ORF.

REPLICATION

1. Virus attaches to host receptors through the S protein (maybe also through HE if present) and is endocytosed into vesicles in the host cell.
2. Fusion of virus membrane with the vesicle membrane (probably mediated by E2), ssRNA(+) genome is released into the cytoplasm.
3. Synthesis and proteolysis of replicase polyproteins. Replicase produces first the complementary ssRNA(-), which will serve as a template for the synthesis of genomic RNA and subgenomic mRNAs.
4. Synthesis of structural proteins encoded by subgenomic mRNAs.
5. Assembly and budding at membranes of the endoplasmic reticulum (ER), the intermediate compartments, and/or the Golgi complex.
6. Release of new virions.