Leviviridae

VIRION

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Non-enveloped, spherical virion about 26 nm in diameter with T=3 icosahedral symmetry composed of 178 CP proteins and a single A maturation protein .
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GENOME

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Monopartite, linear, ssRNA(+) genome about 3.4-4.3 kb in size. The 5' end is a triphosphate. Encodes 3 (Allelovirus) or 4 proteins (Levivirus).

GENE EXPRESSION

The virion RNA is infectious and serves as both the genome and viral messenger RNA. Encodes 4 ORFs. Cp protein represses replicase translation by binding a RNA hairpin at the start site of this gene.
Lysis protein is expressed by suppression of termination of an UGA nonsense codon in Allolevivirus genus.

REPLICATION

  1. Adsorption to F pili of target cells induces cleavage and release of the maturation protein.
  2. Genomic RNA enters the bacterium.
  3. Viral proteins are translated.
  4. Viral replicase assembles with host proteins (ribosomal protein S1, translation elongation factors EF-Tu and EF-Ts) to form the active RNA polymerase.
  5. Replication of genomic RNA into a minus strand, which serves as template to produce new positive strand genomes.
  6. Late in infection CP protein bind to a RNA hairpin on the genome, and new virus particles are assembled in the cytoplasm.
  7. Release by cell lysis.
<div id=PMID:27671640" class="hidden">Asymmetric cryo-EM structure of the canonical Allolevivirus Qbeta reveals a single maturation protein and the genomic ssRNA in situ
Karl V. Gorzelnik, Zhicheng Cui, Catrina A. Reed, Joanita Jakana, Ry Young, Junjie Zhang
Proc. Natl. Acad. Sci. U.S.A. October 11, 2016; 113: 11519-1524