Inter-DNA Attraction Mediated by Divalent Counterions

Xiangyun Qiu, Cornell University
Kurt Andresen, Gettysburg College
Lisa W. Kwok, Cornell University
Jessica S. Lamb, Cornell University
Hye Yoon Park, Cornell University
Lois Pollack, Cornell University

Copyright 2007, The American Physical Society


Can nonspecifically bound divalent counterions induce attraction between DNA strands? Here, we present experimental evidence demonstrating attraction between short DNA strands mediated by Mg2 ions. Solution small angle x-ray scattering data collected as a function of DNA concentration enable model independent extraction of the second virial coefficient. As the [Mg2] increases, this coefficient turns from positive to negative reflecting the transition from repulsive to attractive inter-DNA interaction. This surprising observation is corroborated by independent light scattering experiments. The dependence of the observed attraction on experimental parameters including DNA length provides valuable clues to its origin.