Molecular biology
VIRION
Non-enveloped, flexuous, filamentous, 600-1000 nm or more long and 12-13 nm in diameter.
GENOME
Linear ssRNA(+) genome of 6.5-9 kb in size. The 3’ terminus is polyadenylated and, in some genera, the 5’ end is capped. Encodes for 2 to 6 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 monocistronic subgenomic mRNAs (sgRNAs).
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).
- A negative-sense complementary ssRNA is synthesized using the genomic RNA as a template.
- New genomic RNA is synthesized using the negative-sense RNA as a template.
- Internal subgenomic promoters are used to transcribe the sgRNAs. Traduction of these sgRNAs yields the capsid and movement proteins.
- Formation of new virus particles.