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, ssRNA(+) genome of 12-13kb 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. Enzymes: EndoU ribonuclease
GENE EXPRESSION
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.
Protein GP2 and 5a are produced by leaky scanning from the E and gp5 subgenomic mRNA respectively.
ENZYMES
- RNA-dependent RNA polymerase [P19811]
- Nido-type capping (GDP polyribonucleotidyltransferase, N7methyltransferase, 2'O methylase) [P19811]
- EndoU ribonuclease [P19811]
- Polyprotein major protease (Peptidase S32) [P19811]
- Proteases (Peptidase C31, Peptidase C32, Peptidase C33) [P19811]
- Helicase [P19811]
REPLICATION
CYTOPLASMIC
- 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.
