Competitive Na+ and Rb+ Binding in the Minor Groove of DNA.

Compelling evidence for sequence-dependent intrusion of monovalent, partly dehydrated cations into the minor groove of B-form DNA has come from X-ray crystallography, solution NMR, and molecular dynamics simulations. These findings have received considerable attention, not least because intimate ion association could play a role in sequence-dependent variations of DNA structure. While it has been firmly established that monovalent cations can be directly coordinated to the nucleotide bases in the narrowed AT-tracts in B-DNA duplexes, a quantitative understanding of such specific ion-DNA interactions under physiologically relevant solution conditions is yet to be made clear.