Biological Physics at Cornell: What are the Forces Acting on Nucleic Acids?

An article describing new measurements of the distribution of positively charged ions around DNA double helices in solution has just been published in Physical Review Letters by Lois Pollack's group in collaboration with other scientists at Cornell and Stanford Universities. This type of measurement will allow this group to probe the fundamental physics of DNA-charged ligand interactions. The scattering factors of ions 'condensed' onto the negatively charged DNA strand were modulated using resonant or anomalous scattering techniques. The quality of the data permits quantitative comparisons to atomic-scale models of ion distributions around DNA. These novel measurements are enabled by the development of silicon nitride membranes as low-background windows for x-ray scattering cells.

The intricate folding and biological functions of the highly charged biopolymers RNA and DNA are intimately coupled to the positive counterions that neutralize them. Few data are available that constrain the spatial extent of counterion atmospheres around nucleic acids. In this paper the authors present a new tool to understand the role of the ions based on small-angle X-ray scattering measurements.

Reference: Physical Review Letters, Vol. 90 Article 188103 (2003).