Reproductive Cycle of a Poxvirus in a Host Cell

The replication of the poxvirus occurs in the cytoplasm. The virus is sufficiently complex and has acquired all the functions necessary for genome replication.

The penetration of the virus to the cell is complex and involves more than one mechanism. Two stages of uncoating take place. The outer membrane is removed as the particle enters the cell and in the cytoplasm, and the particle is further uncoated when the core passes into the cytoplasm.

Gene expression is carried out by viral enzymes associated with the core. It is divided into two phases: early genes and late genes.

• Early genes: expressed before genome replication
• Late genes: expressed after genome replication

Late promoters are dependent on DNA replication for activity.

The genome replication of the poxvirus involve self-priming, leading to the formation of high m.w. concatemers that are isolated from infected cells which are subsequently cleaved and repaired to make virus genomes. Thymidine kinase and many other virus-encoded enzymes involved in replication offer potential targets for chemotherapeutic agents.

The assembly occurs in the cytoskeleton. Inclusions are formed in the cytoplasm which matures into virus particles. Actin 'comet tails' are formed and they shoot IEV through the cytoplasm to the cell surface, and then into adjacent cells. This movement has been timed and found to be 3µm/min. This may be instrumental in providing an alternate mechanism for cell to cell transmission. The replication of this large, complex virus is rather quick.

Picture extracted: http://visp.scripps.edu/pox/PoxWebPages/PoxBackground.aspx