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.
Monopartite, linear, 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.
The virion RNA is infectious and serves as both genome and viral messenger RNA. ORF1b is translated by a ribosomal frameshifting. Polyproteins 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. PRRSV, LDV and SHFV also express a truncated polyprotein 1aTF due to a ribosomal frameshifting in the nsp2 gene.
The 3’ proximal region of SHFV contains in addition a large insertion that may encode three additional glycoproteins. Protein GP2 and 5a are produced by leaky scanning from the E and gp5 subgenomic mRNA respectively.
- Attachement to host receptors mediates clathrin-mediated endocytosis of the virus into the host cell.
- Fusion of virus membrane with the endosomal membrane. ssRNA(+) genome is released into the cytoplasm.
- Synthesis and proteolysis of replicase polyproteins.
- Replication occurs in viral factories. A dsRNA genome is synthesized from the genomic ssRNA(+).
- The dsRNA genome is transcribed/replicated thereby providing viral mRNAs/new ssRNA(+) genomes.
- Synthesis of structural proteins encoded by subgenomic mRNAs.
- assembly and ESCRT-independent budding at the membranes of endoplasmic reticulum (ER), intermediate compartments, and/or Golgi complex.
- Release of new virions by exocytosis.