Sobemovirus (taxid:12137)

VIRION

Non enveloped virion, about 30 nm in diameter with a T=3 icosahedral symmetry (180 protein subunits).

GENOME

Monopartite, linear, ssRNA(+) genome of 4 kb. The 5' terminus has a genome-linked protein (VPg). The 3' terminus is not polyadenylated. Some sobemoviruses encapsidate a circular viroid-like satellite RNA (220-390nt).

GENE EXPRESSION

The virion RNA is infectious and serves as both the genome and viral messenger RNA. ORF1 and ORF2 are translated via leaky scanning . ORF2 is a polyprotein which is presumably cleaved into a serine-protease, a VPg and a RdRp protein. The viral serine protease is responsible for all the cleavages. ORF3 is translated via a -1 ribosomal frameshifting. Replication produces a subgenomic RNA which encodes for the capsid protein (ORF4).
Cocksfoot mottle sobemovirus polyprotein is encoded by two different ORFs, the second one is translated via a -1 ribosomal frameshifting. The equivalent of ORF3 is not present.

ENZYMES

• RNA-directed RNA polymerase [RdRp]
• VPG-type capping [VPg]
• Polyprotein major protease (Peptidase S39) [Pro]

REPLICATION

CYTOPLASMIC

1. Virus penetrates into the host cell.
2. Uncoating, and release of the viral genomic RNA into the cytoplasm.
3. The viral RNA is translated to produce replication proteins, ORF2 polyprotein is processed by the viral protease.
4. Replication takes place in cytoplasmic 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 subgenomic RNA encoding for ORF4 capsid protein.
7. Virus assembly.
8. Viral movement protein probably mediates virion cell-to-cell transfer.

Host-virus interaction

Suppression of RNA silencing

Cocksfoot mottle virus P1 protein acts as a suppressor of RNA silencing .