|Title||Salt-Dependent DNA-DNA Spacings in Intact Bacteriophage λ Reflect Relative Importance of DNA Self-Repulsion and Bending Energies|
|Publication Type||Journal Article|
|Year of Publication||2011|
|Authors||X. Qiu, D. C. Rau, A. V. Parsegian, L. T. Fang, C. M. Knobler and W. M. Gelbart|
|Journal Title||Physical Review Letters|
Using solution synchrotron x-ray scattering, we measure the variation of DNA-DNA d spacings in bacteriophage λ with mono-, di-, and polyvalent salt concentrations, for wild-type [48.5×103 base pairs (bp)] and short-genome-mutant (37.8 kbp) strains. From the decrease in d spacings with increasing salt, we deduce the relative contributions of DNA self-repulsion and bending to the energetics of packaged phage genomes. We quantify the DNA-DNA interaction energies within the intact phage by combining the measured d spacings in the capsid with measurements of osmotic pressure in DNA assemblies under the same salt conditions in bulk solution. In the commonly used Tris-Mg buffer, the DNA-DNA interaction energies inside the phage capsids are shown to be about 1kT/bp, an order of magnitude larger than the bending energies.