Molecular biology

VIRION

Enveloped, spherical, about 45-60 nm in diameter. The virion is comprised of an isometric core of 20-30 nm surrounded by a lipid-containing envelope. The RNA genome associates with the N protein to form the nucleocapsid.

GENOME

Monopartite, linear, positive sense, ssRNA genome of 12-16kb in size, capped, and polyadenylated. The leader RNA (65-89 bp) at the 5’ end of the genome is also present at the end of each subgenomic RNAs.

GENE EXPRESSION

The virion RNA is infectious and serves as both 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. The mRNA2 is bicistronic.
The 3’ proximal region of SHFV contains in addition a large insertion that may encode three additional glycoproteins.

REPLICATION

CYTOPLASMIC

1. Virus attaches to host receptors and is endocytosed into vesicles in the host cell.
2. Fusion of virus membrane with the vesicle membrane; 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.