Secoviridae

VIRION

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Non-enveloped, 25-30 nm in diameter, T=pseudo3 icosahedral capsid. The three jell rolls, which are characteristic of picornavirales capsid proteins (CP), can be present in one large CP with 3 jelly rolls domains, two CP (one large with two jelly rolls domains and one small a single domain), or three CP.

GENOME

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Segmented, bipartite linear ssRNA(+) genome composed of RNA-1=6-8 kb and RNA-2=4-7 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 one or two capsid proteins and product(s) involved in cell-to-cell movement.

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.