VIRION
Non enveloped virion, about 30 nm in diameter with a T=3 icosahedral symmetry (180 protein subunits).
GENOME
Monopartite, linear, ssRNA(+) genome of about 4-5 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).
ENZYMES
- RNA-directed RNA polymerase [RdRp]
- VPG-type capping [VPg]
- Polyprotein major protease (Peptidase S39) [Pro]
REPLICATION
CYTOPLASMIC
- Virus penetrates into the host cell.
- Uncoating, and release of the viral genomic RNA into the cytoplasm.
- The viral RNA is translated to produce replication proteins, ORF2 polyprotein is processed by the viral protease.
- Replication takes place in cytoplasmic viral factories. A dsRNA genome is synthesized from the genomic ssRNA(+).
- The dsRNA genome is transcribed/replicated thereby providing viral mRNAs/new ssRNA(+) genomes.
- Expression of the subgenomic RNA encoding for ORF4 capsid protein.
- Virus assembly.
- Viral movement protein probably mediates virion cell-to-cell transfer.