Salt-Dependent DNA-DNA Spacings in Intact Bacteriophage Lambda Reflect Relative Importance of DNA Self-Repulsion and Bending Energies

Abstract

Using solution synchrotron x-ray scattering, we measure the variation of DNA-DNA d spacings in bacteriophage Lambda with mono-, di-, and polyvalent salt concentrations, for wild-type [48500 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
PRL 106 028102 (2011)

Authors

Xiangyun Qiu, Donald C. Rau, V. Adrian Parsegian, Li Tai Fang, Charles M. Knobler, and William M. Gelbart