Molecular biology

VIRION

Non-enveloped, flexuous, filamentous virion, about 720 nm long and 12-13 nm in diameter.

GENOME

Linear ssRNA(+) genome of about 7 kb in size. The 3’ terminus is polyadenylated and the 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 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 probably used to transcribe the sgRNAs. Traduction of these sgRNAs yields the capsid protein as well as other proteins.
7. Formation of new virus particles.