Molecular biology

VIRION

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

GENOME

Linear ssRNA(+) genome of 6.8 kb in size. The 5’ end may possibly be capped and 3’ terminus is polyadenylated. Encodes for 2 ORFs.

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 by readthrough of a ‘leaky’ stop codon between the helicase and RdRp regions. The capsid (coat) protein is transcribed presumably as a monocistronic subgenomic mRNA (sgRNA).

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 is used to transcribe the sgRNA. Traduction of this sgRNA yields the capsid protein.
7. Formation of new virus particles.