Saetivirus

VIRION

Non-enveloped, rod of filaments of 7 nm in diameter and 1000 to 1200nm long in length. Helical capsid with adsorption proteins on one end.

GENOME

Circular, ssDNA genome (+) of 6.3 to 7.5 kb encoding for 12 to 15 proteins. Replication occurs via dsDNA intermediate and rolling circle.

GENE EXPRESSION

Each gene is transcribed by host cellular machinery, via a specific promoter. Some genes end by a transcription terminator.



REPLICATION

CYTOPLASMIC

  1. Virus mediates pilus-mediated adsorption of the virus onto host cell. Pilus retraction pulls the virion to the host internal membrane.
  2. The proteins of the capsid perform the injection of the viral DNA through bacterial membranes into cell cytoplasm.
  3. Host polymerase convert the (+)ssDNA viral genome into a covalently closed dsDNA called replicative form DNA (RF).
  4. dsDNA transcription by host RNA polymerase gives rise to viral mRNAs.
  5. A viral protein may nick RF DNA strand at the origin of replication.
  6. (+) strand replication occurs by rolling circle.
  7. New (+)ssDNA genomes are converted into new RF molecules, and further transcription occurs.
  8. A conversion into RF dsDNA is inhibited, as neo-synthesized genomic ssDNA is covered with a viral protein.
  9. Assembly of the viral capsid.
  10. New virions are secreted from host cell.
  11. Infected cells continue to divide and produce virions indefinitely.