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Updated: Jul 29, 2026
Combining Single-molecule Manipulation and Imaging for the Study of Protein-DNA Interactions
Published on: August 27, 2014
Spatial distribution of competing ions around DNA in solution
1School of Applied and Engineering Physics, Cornell University, Ithaca, New York 14853, USA.
Abstract:
The competition of monovalent and divalent cations for proximity to negatively charged DNA is of biological importance and can provide strong constraints for theoretical treatments of polyelectrolytes. Resonant x-ray scattering experiments have allowed us to monitor the number and distribution of each cation in a mixed ion cloud around DNA. These measurements provide experimental evidence to support a general theoretical prediction: the normalized distribution of each ion around polyelectrolytes remains constant when ions are mixed at different ratios. In addition, the amplitudes of the scattering signals throughout the competition provide a measurement of the surface concentration parameter that predicts the competition behavior of these cations. The data suggest that ion size needs to be taken into account in applying Poisson-Boltzmann treatments to polyelectrolytes such as DNA.
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