Poxvirus replication cycle

  • Virus entry:
    • Extracellular virions can enter by macropinocytosis or by direct entry at the cell surface. Host receptors are unknown. Macropinocytosis can involve apoptotic mimicry
  • Transcription in cytoplasmic factories
    • early: Viral replication machinery, host-modulating factors, core-associated enzymes and extracellular virion membrane proteins (about 118 genes in vaccinia virus)
    • Postreplicative events:
      • Intermediate:DNA binding/packaging and core-associated nonenzymatic proteins (53 Genes in vaccinia virus)
      • late: redox disulfide bond enzymes, virion morphogenesis, crescent formation proteins, mature virion membrane proteins and components of the entry-fusion complex (38 genes in vaccinia virus)
  • Virion assembly
  • virus exit

Important: Poxvirus genes are transcribed in the cytoplasm by viral enzymes and are not spliced because there are no splicing machinery outside the nucleus. If they were expressed from a plasmid in the nucleus, artefacts could result from mRNA splicing.
The surface proteins of mature virions are not expressed in the endoplasmic reticulum of the cell, and the disulfide bonds are made by a viral sulfohydryl-oxidase in the cytoplasm. Expression of these proteins from plasmids can lead to artefacts.
Acknowledgement: Thanks for the help of Rich Condit, Nissin Moussatche and Bernard Moss.