Molecular biology

VIRION

Non-enveloped, flexuous, filamentous,470-1000 nm or more long and 12-13 nm in diameter.

GENOME

Linear ssRNA(+) genome of 5.8-9 kb in size. The 3’ terminus is polyadenylated and, in some genera, the 5’ end is capped. Encodes for 3 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

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 as a monocistronic mRNA to produce the RdRp (encoded by the 5’-proximal ORF).
4. A negative-sense complementary ssRNA is synthesized using the genomic RNA as a template.
5. New genomic RNA is synthesized using the negative-sense RNA as a template.
6. Internal subgenomic promoters are used to transcribe the sgRNAs. Traduction of these sgRNAs yields the capsid and movement proteins.
7. Formation of new virus particles.