Cripavirus (taxid:144051)

VIRION

Non enveloped, pseudo T=3 icosahedral capsid, about 30 nm in diameter.

GENOME

Monopartite, linear ssRNA(+) genome of 8.5-10.2 kb, with a VPg bound at the 5'-terminus and a 3'-polyA tract. Contains two non-overlapping open reading frames, ORF1 and ORF2, which respectively encode the nonstructural and structural proteins.

GENE EXPRESSION

The virion RNA is infectious and serves as both genome and mRNA. The genome ORF1 and ORF2 encode two polyproteins, the first of which contains the non-structural proteins involved in replication, while the second, contains four capsid proteins. Each ORF is preceded by an internal ribosome entry site (IRES) located at the 5' end and at the intergenic region (IGR) between the two ORFs. Tha IGR IRES allows translation of ORF2 at a non-AUG codon.
Ribosomal skipping may also be used to express viral protein 1A from ORF1 of cricket paralysis virus.

ENZYMES

• RNA-dependent RNA polymerase [RdRp Q9IJX4]
• VPG-type capping [VPg Q9IJX4]
• NTPase-helicase [NTPase Q9IJX4]
• Polyprotein major protease (Peptidase C3) [Protease-Pol Q9IJX4]

REPLICATION

1. Virus penetrates into the cell.
2. Uncoating, and release of the viral genomic RNA into the cytoplasm.
3. Synthesis and proteolytic cleavage of the replicase polyprotein RNA1.
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. Expression of the RNA2 polyprotein (structural proteins).
7. virus release (or cell-cell spread of viral RNAs?).

Host-virus interaction

Host gene expression shutoff by virus

CrPV infection results in host translation shutoff concomitant with an increase in viral protein synthesis via CrPV internal ribosome entry sites (IRES). Host translation shutoff involves the dissociation of eIF4G and eIF4E .

Suppression of RNA silencing

Drosophila C virus protein DCV-1A and Cricket paralysis virus protein CrPV-1A function as suppressor of RNA silencing .