Competitive Na+ and Rb+ binding in the minor groove of DNA

New 23Na and 87Rb magnetic relaxation dispersion (MRD) data that demonstrate competitive and long-lived binding of Na+ and Rb+ ions in the minor groove of the B-DNA duplex [d(CGCGAATTCGCG)]2 are presented. The ion occupancies derived from the MRD data are substantially higher than previously reported, suggesting that groove-bound ions significantly influence the energetics and structural polymorphism of DNA in vivo.