Archive for June 5th, 2012

Differential assembly of Hepatitis B Virus core protein on single- and double-stranded nucleic acid suggest the dsDNA-filled core is spring-loaded

5 June, 2012

See on Scoop.itVirology and Bioinformatics from Virology.ca

“Hepatitis B Virus (HBV) cores assemble on viral RNA, which is reverse transcribed within the core to the partially dsDNA genome of mature HBV. However, constraining dsDNA, a stiff polymer, within a core necessarily requires far greater capsid stability than constraining ssRNA. We hypothesized that, unlike ssRNA, dsDNA would be a poor substrate for assembly. We examined titrations of ssDNA and dsDNA with purified HBV core protein, Cp183, by EMSA, EM, DLS, and etheno-DNA fluorescence. Cp183 bound ssDNA with high affinity to form virus-like capsids. However, Cp183 bound dsDNA poorly, forming a mixture of irregular complexes. Nonetheless, we observed some normal cores in dsDNA assembly reactions, indicating that the energy required to bend DNA could be similar to the protein–protein association energy. This similarity of energies suggests that dsDNA stresses mature HBV cores, in agreement with calculation, which may be the basis for the virus maturation signal and DNA release.”

 

A great paper – and one which harks back to an age where many studies on viruses were biophysical, because the molecular biological techniques we use now had simply not been invented.  I note frequent reference to Bancroft, 1970 – to a paper on self-assembly of plant viruses.  I also like the concept of HBV cores as a Jack-in-a-box: ready to pop open to deliver the goodies.

See on www.sciencedirect.com

Endogenous RNA viruses of plants in insect genomes

5 June, 2012

See on Scoop.itVirology News

“Endogenous viral elements (EVEs) derived from RNA viruses with no DNA stage are rare, especially those where the parental viruses possess single-strand positive-sense (ssRNA +) genomes. Here we provide evidence that EVEs that share a sequence similarity to ssRNA + viruses of plants are integrated into the genomes of a number of insects, including mosquito, fruit flies, bees, ant, silkworm, pea aphid, Monarch butterfly, and wasps. A preliminary phylogenetic analysis places these EVEs as divergent relatives of the Virgaviridae and three currently unclassified plant viral species.”

I have covered this before, in ViroBlogy, (and here, in 2007)as an interesting and probably under-appreciated phenomenon.  I note Eddie Holmes and colleagues have now taken it much, much further – which incidentally lends significant credence to my supposition that virus/vector/plant coevolution was probably a fair bit more intimate than has been supposed, with the newly-emerged (in evolutionary terms) insects and their viruses meeting terrestrial plants and THEIR viruses.  And mixing everything up, as I have speculated elsewhere (Origins of Viruses).

I thank Jean-Marie Verchot for drawing my attention to this!

See on www.sciencedirect.com