Abstract: | It has been inferred from previous studies that Mn2+ ions bind preferentially to G·C base pairs in DNA, and it has even been suggested that this preference for G·C pairs might be responsible for some of the Mn2+ specific effects observed in various biochemical reactions. In this paper we investigate the AT/GC preference of Mn2+ by direct competition studies in which AT-rich DNA was dialyzed against GC-rich DNA in the presence of varying amounts of Mn2+. Analysis of these results demonstrates that over a wide range of Mn2+/DNA(P) molar ratios, Mn2+ binds to A·T and to G·C base pairs with virtually identical affinity, although in a somewhat different mode. Both the present and previous nmr, uv, CD, and melting studies are discussed in terms of the different modes of binding of Mn2+ to single- and double-stranded DNA. |