The DNA structure responds differently to physiological concentrations of K+ or Na+

The influence of monovalent cations on DNA conformation and readout is an open question. This NMR study of DNA with either Na+ or K+ at physio logical concentrations shows that the nature of the cation affects the P-31 chemical shifts (delta P) and the sequential distances H2'(l)-H6/8(i+1),H2(l)()--H68(i+1), and H6/8(i)-H6/8(i+1). The delta P and distance variations ascertain that the nature of the cation affects the DNA overall structure, i.e. both the conformational equilibria between the backbone BI (epsilon-zeta < 0 degrees) and BII (epsilon-zeta > 0 degrees) states and the helical parameters, via their strong mechanical coupling. These results reveal that Na+ and K+ interactions with DNA are different and sequencedependent. These ions modulate the overall intrinsic properties of DNA, and possibly its packaging and readout. (C) 2007 Elsevier Ltd. All rights reserved.