Poxviruses practice DNA replication solely in the cytoplasm. This is possible because poxvirus genomes encode enzymes required for transcription and replication. Some of these enzymes carried in the virion include DNA-dependent RNA polymerase, poly [A] polymerase, capping enzyme, methylating enzymes, and a transcription factor. Through endocytosis, the viral core is released into the cytoplasm where the viral transcriptase intiates transcription. It is important to note that an RNA polymerase II subunit from the nucleus is required. Capped and polyadenylated, unspliced mRNAs are made quickly, and are vital to transcribe the "early genes". The early genes code for proteins including DNA polymerase, thymidine kinase. Once DNA replication has commenced (it is believed at both ends),"immediate early" and "late" genes will be transcribed. The virions of the new viruses are assembled in allocated areas of the cytoplasm, and the virion's outer membrane and the outer bilayer fuse. While some of the immature virions go to the Golgi complex where they acquire an envelope via exocytosis, others are simply released from the cell.

Interestingly,once a cell is infected, there is a development of inclusion bodies. Also, poxviruses have genes that code for proteins that affect the host's immune response to infection by the secretion of these products from infected cells. These "virokines" include some conferring resistance to interferon, a homolog of an epidermal growth factor, as well as a complement regulatory protein. Other proteins are thought to interfere with the function of some cytokines.

Diagram illustrating the replication cycle of poxviruses

*Special thanks to the creators of "http://www-micro.msb.le.ac.uk/335/Poxviruses.html" for the creation of this image

Back to Pox Home Page