Many viruses, whether they infect bacteria, plants or animals, are adept at packing long stretches of nucleic acid (DNA or RNA) within their nanometer-sized protein shells. In many of the viruses that contain double-stranded DNA, the DNA gets packaged so tightly that it bends upon itself, resulting in repulsive forces that exert a tremendous amount of pressure on the virus's outer shell, indicating a great amount of stored energy. At the moment of infection, when the DNA is being shot out of the virus, the energy stored in the tightly packed DNA is released and converted into thermal energy.
Evilevitch and his colleagues from Lund University in Sweden, where Evilevitch was previously employed, and the Universite de Lyon in France used an experimental technique known as isothermal titration calorimetry (ITC) to directly measure the heat, and thus the thermal energy, released during viral genome ejection. Until now, only indirect measurements of this energy have been available. They describe this new method in the Feb. 5 issue of the Journal of Molecular Biology.
"We are the first group to use titration calorimetry to study genome release from viruses," Evilevitch said. "In this study, we looked at viruses that infect bacteria, called bacteriophages, as an experimental model system, but ITC can also be applied to other types of viruses. We're currently investigating the rotavirus, which causes stomach flu, using our new technique."
In the Journal of Molecular Biology report, Evilevitch used ITC to measure the thermal energy released during genome ejection, which is the same as the stored internal energy that results from genome packaging. His results, which agree with analytical models and computer simulations, show that the heat released increases as DNA length increases. He also discovered that
|Contact: Jocelyn Duffy|
Carnegie Mellon University