Votavová H, Sponar J
Institute of Organic Chemistry and Biochemistry, Czechoslovak Academy of Sciences, Prague.
J Biomol Struct Dyn. 1988 Apr;5(5):981-95. doi: 10.1080/07391102.1988.10506444.
AB-X transition of polyh(dA-dT).poly(dA-dT) was observed to occur in methanol-water mixtures with methanol concentrations higher than 50% in the presence of a specific combination of monovalent and divalent cations. In the presence of Na+, divalent cations induce denaturation of poly(dA-dT).poly(dA-dT) accompanied by condensation and/or aggregation, and effect similar to that observed previously with random sequence DNA (Votavová, Kucerová, Felsberg and Sponar, J. Biomol. Struct. Dyn. 4,477-489, 1986). In the presence of Cs+ cations a B-X transition was induced by addition of Ca2+ or Mn2+ but not Mg2+ or Ni2+ ions. Circular dichroism and ultraviolet spectroscopy demonstrate that the X conformation is a double stranded form of poly(dA-dT).poly(dA-dT) belonging presumably to the B family which, however has an altered base stacking. The X conformation of poly(dA-dT).poly(dA-dT) found in methanol-water mixtures is a condensed and/or aggregated form. In contrast, the X conformation characterized by similar CD spectra observed in high salt concentrations is not aggregated up to a concentration of 6 M CsF. In methanol-water mixtures (A+T)-rich bacterial DNA behaves essentially as a random sequence DNA revealing no detectable amount of the X form. On the other hand crab (Cancer pagurus) satellite and crab non-satellite DNAs containing varying amounts of (dA-dT)n.(dA-dT)n sequences were shown to undergo a B-X transition, at least partly, in both methanol-water mixtures and 6 M CsF solutions.
在一价和二价阳离子的特定组合存在下，当甲醇浓度高于50%时，观察到聚（dA-dT）·聚（dA-dT）发生AB-X转变。在Na⁺存在的情况下，二价阳离子会诱导聚（dA-dT）·聚（dA-dT）变性，并伴随着凝聚和/或聚集，其效应与之前在随机序列DNA中观察到的相似（Votavová、Kucerová、Felsberg和Sponar，《生物分子结构与动力学杂志》4，477 - 489，1986）。在Cs⁺阳离子存在的情况下，添加Ca²⁺或Mn²⁺会诱导B-X转变，但添加Mg²⁺或Ni²⁺则不会。圆二色性和紫外光谱表明，X构象是聚（dA-dT）·聚（dA-dT）的双链形式，大概属于B家族，但其碱基堆积发生了改变。在甲醇-水混合物中发现的聚（dA-dT）·聚（dA-dT）的X构象是一种凝聚和/或聚集的形式。相比之下，在高盐浓度下观察到的具有相似圆二色谱的X构象，在浓度高达6 M CsF时都不会聚集。在甲醇-水混合物中，富含（A+T）的细菌DNA的行为基本上与随机序列DNA相同，未检测到X形式。另一方面，含有不同量（dA-dT）n·（dA-dT）n序列的蟹（黄道蟹）卫星DNA和蟹非卫星DNA在甲醇-水混合物和6 M CsF溶液中都至少部分发生了B-X转变。
