Molecular biology

VIRION

Non-enveloped, flexuous, filamentous, about 960 nm long and 12 nm in diameter.

GENOME

Linear ssRNA(+) genome of 8.7 kb in size. The 5’ end is capped and 3’ terminus is polyadenylated. Encodes for 3 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. The putative movement protein (ORF2) and capsid (ORF3) proteins are transcribed from 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 sgRNA yields the capsid protein and the putative movement protein.
7. Formation of new virus particles.