Coman Daniel, Russu Irina M
Department of Chemistry and Molecular Biophysics Program, Wesleyan University, Middletown, CT 06459, USA.
Nucleic Acids Res. 2004 Feb 9;32(3):878-83. doi: 10.1093/nar/gkh228. Print 2004.
Proton exchange and NMR spectroscopy have been used to define the effects of Mg2+ ions upon the stability of individual base pairs in the intramolecular parallel triple helix formed by the DNA oligonucleotide d(GAAGAGGTTTTTCCTCTTCTTTTTCTTCTCC). The rates of exchange of individual Watson-Crick and Hoogsteen imino protons in the DNA triple helix were measured in the absence and in the presence of Mg2+ ions. The results reveal that Mg2+ lowers the exchange rates of most imino protons in the structure by stabilizing the corresponding base pairs in their native closed conformation. Comparison of the DNA triple helix containing Na+ counterions to the same helix containing Mg2+ counterions shows that these stabilizing effects result, in large part, from Mg2+ ions closely associated with the DNA. Moreover, the effects are site-specific and depend on the number and location of protonated cytosines relative to the observed base. These findings provide new insights into the molecular roles of C+*GC triads in determining the stability of DNA triple-helical structures.
质子交换和核磁共振光谱已被用于确定镁离子对由DNA寡核苷酸d(GAAGAGGTTTTTCCTCTTCTTTTTCTTCTCC)形成的分子内平行三链螺旋中单个碱基对稳定性的影响。在不存在和存在镁离子的情况下,测量了DNA三链螺旋中单个沃森-克里克和 hoogsteen亚氨基质子的交换速率。结果表明,镁离子通过稳定相应碱基对的天然闭合构象,降低了结构中大多数亚氨基质子的交换速率。将含有钠离子反离子的DNA三链螺旋与含有镁离子反离子的同一螺旋进行比较表明,这些稳定作用在很大程度上是由与DNA紧密结合的镁离子导致的。此外,这些作用具有位点特异性,并且取决于质子化胞嘧啶相对于观察到的碱基的数量和位置。这些发现为C+*GC三联体在确定DNA三链螺旋结构稳定性中的分子作用提供了新的见解。