Re: Reply to Morrell: Regarding 'endogenous entities' and 'epiphenomena' 19 February 2005
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Nicholas Bennett,
Infectious Disease Postdoc/Clinician
Department of Pediatrics, University Hospital, Syracuse, NY

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Re: Re: Reply to Morrell: Regarding 'endogenous entities' and 'epiphenomena'

I simply had to write upon reading Mr Russell's statement that:

"Most viruses replicate in the cytoplasm."

Sadly if he had some form, any form, of education in the field he would know better.

RNA viruses (with the exception of the retroviruses which must integrate) do largely replicate in the cytoplasm, since this is far easier than trying to enter the nuclear membrane and there are reasonable numbers of free ribonucleotides in the cytoplasm. RNA viruses also tend to encode their own polymerases, and so can make mRNA's or rough equivalents without using the cellular RNA polymerase II. The cell is there largely as an ATP supply and source of amino and nucleic acids, and membrane (as appropriate).

DNA viruses on the other hand require considerable quantities of deoxyribonucleotides and furthermore often use the cellular DNA polymerase, making nuclear entry a paramount feature of their replication strategy. They also need some way to make mRNA, and RNA pol II is only in the nucleus. Such viruses include adenovirus, papilloma virus, the herpes viruses, parvovirus etc. Since the nuclear membrane is removed during mitosis, and deoxyribonucleotide production is increased, many DNA viruses induce cell cycling - this is why they are more frequently associated with cancers.

The one exception, which is an exception to most "rules" of virology, is the pox virus family. These behemoths are DNA viruses but encode their own DNA and RNA polymerase and an entire deoxyribonucleotide production plant, and so can replicate in the cytoplasm.

Nick Bennett njb35@cantab.net

Competing interests: None declared