Caulimovirus

VIRION

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Non enveloped, large (50 nm diameter) icosahedral particles composed of 420 subunits with a T=7 symmetry . The virion shell is covered with virion associated protein (VAP) . It has not been described whether handedness of capsid is laevo or dextro, here the pictures dsplays a laevo form.

GENOME

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Monopartite, open circular, double stranded DNA of about 8000 base pairs with discontinuities in both strands: one in the transcribed strand and one to three in the non-transcribed strand. Codes for 6 to 7 proteins.

GENE EXPRESSION

The 35s RNA and its spliced derivatives serves as polycistronic mRNA for viral proteins. Polycistronic translation depends on Tav which is believed to be a translation reinitiation factor. Tav is produced from the monocistronic 19S RNA, the second major viral transcript. Translation of 35S RNA is initiated by ribosome shunt, in which scanning ribosomes bypass leader sequence and multiple short ORFs.

REPLICATION

CYTOPLASMIC / NUCLEAR

  1. Attachment of the viral proteins to host receptors mediates its entry into the host cell.
  2. The viral dsDNA is released into the nucleus where it is transcribed by host RNA polymerase II
  3. 35S RNA and 19S RNA translation produces viral proteins.
  4. 35S RNA is retrotranscribed in the cytoplasm into new dsDNA genomes
  5. Genomes are encapsidated with capsid protein, releasing new virions.