Alphanodavirus (taxid:143920)

VIRION

Non enveloped virion, about 30 nm in diameter with a T=3 icosahedral symmetry (180 protein subunits). RNA1 and RNA2 are copackaged into the same virion and both are required for infectivity.

GENOME

Segmented, bipartite linear ssRNA(+) genome composed of RNA1=3.1 kb and RNA2=1.4 kb. Each genome segment 5' end is capped. The 3'end has no poly (A) tract.

GENE EXPRESSION

The virion RNA is infectious and serves as both the genome and viral messenger RNA. RNA1 encodes directly the RNA-dependent RNA polymerase (protein A), and RNA2, the capsid protein. A subgenomic RNA (sgRNA3), 3' co-linear to RNA1 is also produced and encode proteins B1 and B2.

ENZYMES

• RNA-dependent RNA polymerase [RdRp]
• Alphavirus-type capping:
  • RNATPase [RdRp]
  • N7 MTase [RdRp]
  • GTase [RdRp]
  • 2'O MTase ?
• Self-cleavage capsid (Peptidase N1) [Capsid alpha]

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-1 is translated to produce the RdRp protein.
4. Replication takes place in cytoplasmic viral factories. A dsRNA genome is synthesized from the genomic ssRNA(+).
5. The dsRNA genome is transcribed/replicated thereby providing viral mRNAs/new ssRNA(+) genomes.
6. Expression of the subgenomic RNA-3.
7. Translation of RNA-2 encoding capsid protein alpha.
8. Virus assembly in the cytoplasm around genomic RNA1 and RNA2.
9. Assembled capsid protein alpha is cleaved into capsid protein beta and gamma.
10. Release of infectious particles (lysis?).

Host-virus interaction

Suppression of RNA silencing

Nodamuravirus protein B2 and Flock house virus protein B2 act as suppressors of RNA silencing .