Cremegaviridae (taxid:2732894)

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 17kb in size, capped, and polyadenylated.

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. 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.

ENZYMES

• RNA-dependent RNA polymerase [Q04561]
• Nido-type capping (GDP polyribonucleotidyltransferase, N7methyltransferase, 2'O methylase) [Q04561]
• EndoU ribonuclease [Q04561]
• Polyprotein major protease (Peptidase S32) [Q04561]
• Proteases (Peptidase C31, Peptidase C32, Peptidase C33) [Q04561]
• Helicase [Q04561]

REPLICATION

CYTOPLASMIC

1. Attachement to host receptors mediates clathrin-mediated endocytosis of the virus into the host cell.
2. Fusion of virus membrane with the endosomal membrane. ssRNA(+) genome is released into the cytoplasm.
3. Synthesis and proteolysis of replicase polyproteins.
4. Replication occurs in viral factories. A dsRNA genome is synthesized from the genomic ssRNA(+).
5. The dsRNA genome is transcribed/replicated thereby providing viral mRNAs/new ssRNA(+) genomes.
6. Synthesis of structural proteins encoded by subgenomic mRNAs.
7. assembly and ESCRT-independent budding at the membranes of endoplasmic reticulum (ER), intermediate compartments, and/or Golgi complex.
8. Release of new virions by exocytosis.