VIRION
Non-enveloped, quasi-spherical virion about 29nm in diameter with T=3 icosahedral symmetry composed of 180 coat proteins: 12 pentamers and 20 hexamers.
GENOME
Segmented, tripartite linear ssRNA(+) genome composed of RNA1, RNA2, RNA3. Each genomic segment has a 3' tRNA-like structure and a 5'cap.
GENE EXPRESSION
Genomic RNA serves as messenger RNAs. RNA1 and RNA2 encode respectively proteins 1a and 2a, both involved in genome replication and internal transcription of sgRNA4 from the minus-strand copy of RNA3. RNA3 and sgRNA4 are translated respectively into movement and capsid proteins. ORF2b encodes a viral suppressor of RNA silencing (VSR) and is expressed as a subgenomic RNA (sgRNA4A).
ENZYMES
REPLICATION
CYTOPLASMIC
- Virus penetrates into the host cell.
- Uncoating, and release of the viral genomic RNA into the cytoplasm.
- Expression of protein 1a and 2a to produce replication proteins.
- Replication occurs in viral factories made of membrane vesicles derived from the ER (spherules). A dsRNA genome is synthesized from the genomic ssRNA(+).
- The dsRNA genome is transcribed/replicated thereby providing viral mRNAs/new ssRNA(+) genomes.
- Subgenomic RNA4 is translated producing capsid proteins.
- Assembly of new virus particles.
- Viral movement protein triggers the formation of tubular structures that mediate virion cell-to-cell transfer via a tubule-guided mechanism.