Regarding the infectivity of naked DNA

[ae at dna.bio.warwick.ac.uk]

In article ED at molbiol.uct.ac.za ("Ed Rybicki") writes:
>Ahem...if a plant virologist has heard of cDNA clones of 
>picornaviruses being infectious if introduced into cells, AND of 
>"naked DNA" vaccines - injections of cloned DNA directly into muscle 
>tissue leading to protein production and subsequent immunity to an 
>infectious agent - then so should you...!  And it means that DNA 
>copies of an RNA virus could be infectious, as has (I think) been 
>shown for retroviruses.

The observation for retroviruses is perhaps understandable since they have 
a DNA intermediate from which a functional mRNA can be generated by host cell 
transcritional processes.  The production of positive sense RNA requires 
transcription from the DNA and this is usually achieved by placing a promoter 
at an appropriate point in the DNA.  It is conceptually easy to see how this 
might generate a genomic copy of a picornavirus which could produce replicase 
enzyme and initiate a productive infection.  The same cannot be said for a 
negative sense virus (such as Ebola) for which the RNA of either sense cannot 
replicate without the presence of specific virus proteins, especially the 
polymerase.  The positive sense RNA of such viruses cannot be used to generate 
protein as far as is known.  (This excludes the arenaviruses and bunyaviruses 
in which particular segments are ambisense).  If such a process were possible 
it would certainly make life easier in the negative sense RNA field.

Andrew Easton