Betatetravirus (taxid:85650)

VIRION

Non-enveloped virion, about 40 nm in diameter with a T=4 icosahedral symmetry (240 copies of two proteins derived from the capsid precursor cleavage). The capsid precursor is expressed from a subgenomic RNA molecule which, along with genomic RNA, can be packaged into virions.

GENOME

Linear ssRNA(+) genome of 6.5 kb. The 5' terminus is not capped, and the 3' terminus is not polyadenylated but terminates with a distinctive tRNA-like structure.

GENE EXPRESSION

The virion RNA is infectious and serves as both the genome and viral messenger RNA. Genomic RNA is translated into a polyprotein which is cleaved presumably by a viral protease into replication proteins. Replication produces a subgenomic RNA which encodes for capsid protein.

ENZYMES

• RNA-dependent RNA polymerase [RNA polymerase]
• Alpha type capping
  • RNA TPase ?
  • N7 MTase [RNA polymerase]
  • GTase ?
  • 2'O MTase ?
• Asparagine proteases (Peptidase N2) [Capsid]

REPLICATION

CYTOPLASMIC

1. Virus penetrates into the host cell.
2. Uncoating, and release of the viral genomic RNA into the cytoplasm.
3. Genomic RNA is translated to produce replication proteins.
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 encoding the capsid protein.
7. Assembly of new virus particles.
8. Virion maturation by the viral protease.