Nepovirus (taxid:12270)

VIRION

Non-enveloped, 28-30 nm in diameter, pseudo T=3 icosahedral capsid. The large capsid protein (CP) contains the 3 jelly rolls domains characteristic of the picornavirales . Genomic RNAs are encapsidated separately into two different types of particle similar in size.

GENOME

Segmented, bipartite linear ssRNA(+) genome composed of RNA-1=7.5 kb and RNA-2=3.9 kb. Each genomic segment has a VPg linked to its 5' end and a 3' poly(A) tract.

GENE EXPRESSION

The virion RNA is infectious and serves as both the genome and mRNA.
RNA-1 and RNA-2 are translated into two polyproteins, which are then processed into functional proteins. RNA-1 encodes proteins necessary for replication, while RNA-2 encodes for capsid protein and product(s) involved in cell-to-cell movement.

ENZYMES

• RNA-dependent RNA polymerase [RdRp]
• VPG-type capping [VPg]
• NTPase-helicase [Hel]
• Polyprotein major protease (Peptidase C3) [Pro]

REPLICATION

CYTOPLASMIC

1. Virus penetrates into the cell.
2. Uncoating, and release of the viral genomic RNA into the cytoplasm.
3. Synthesis and proteolytic cleavage of the replicase polyprotein RNA-1.
4. Replication occurs in viral factories made of membrane vesicles derived from the ER. A dsRNA genome is synthesized from the genomic ssRNA(+).
5. The dsRNA genome is transcribed/replicated thereby providing viral mRNAs/new ssRNA(+) genomes.
6. Assembly of new virus particles.
7. Movement protein allows cell-to-cell movement.