VIRION
Non-enveloped, flexuous, filamentous,800 nm or more long and 12-13 nm in diameter.
GENOME
Linear ssRNA(+) genome of 8.4-9.3 kb in size. The 3' terminus is polyadenylated and 5'end is capped. Encodes for 5 proteins.
GENE EXPRESSION
The virion RNA is infectious and serves as both the genome and viral messenger RNA. RNA-dependent RNA polymerase (RdRp) is translated directly from the genomic RNA. The other ORFS are transcribed presumably as subgenomic mRNAs (sgRNAs).
ENZYMES
- RNA-dependent RNA polymerase [Polyprotein]
- Alpha-type capping [Polyprotein]
- Polyprotein major protease (Peptidase C23) [Polyprotein]
REPLICATION
CYTOPLASMIC
- Virus penetrates into the host cell.
- Uncoating, and release of the viral genomic RNA into the cytoplasm.
- The viral RNA is translated as a monocistronic mRNA to produce the RdRp (encoded by the 5'-proximal ORF).
- 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.
- Internal subgenomic promoters are used to transcribe the sgRNAs. Traduction of these sgRNAs yields the capsid and movement proteins.
- Assembly of new virus particles.
- Triple gene block proteins (TGBp) allow cell-to-cell and long-distance movement.