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
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