Malkov V A, Voloshin O N, Veselkov A G, Rostapshov V M, Jansen I, Soyfer V N, Frank-Kamenetskii M D
Institute of Molecular Genetics, Russian Academy of Science, Moscow.
Nucleic Acids Res. 1993 Jan 11;21(1):105-11. doi: 10.1093/nar/21.1.105.
We have studied a protonated pyrimidine-purine-purine (Py-Pu-Pu) triplex, which is formed between the d(C)nd(G)n duplex and the d(AG)m oligonucleotide as the third strand and carries the CGA+ protonated base-triads. We have observed such an intermolecular complex between a plasmid carrying the d(C)18 d(G)18 insert and the d(AG)5 oligonucleotide without bivalent cations in 200 mM of Na+ at pH4.0. Bivalent cations additionally stabilize the complex. We propose the structures for nearly isomorphous base-triads TAA, CGG and CGA+. To identify the H-DNA-like structure, which includes the triplex between d(C)n d(G)n duplex and the AG-strand, we have cloned in a superhelical plasmid the insert: G10TTAA(AG)5. The data on photofootprinting and chemical modification with diethyl pyrocarbonate, potassium permanganate and dimethyl sulfate demonstrate that the H-like structure with triplex carrying CGG and CGA+ base triads is actually formed under acid conditions. In the course of this study we have come across unexpected results on probing of Py-Pu-Pu triplexes by dimethyl sulfate (DMS): the protection effect is observed not only for guanines entering the duplex but also for guanines in the third strand lying in the major groove. We have demonstrated this effect not only for the case the novel protonated Py-Pu-Pu triplex but also for the traditional non-protonated Py-Pu-Pu intramolecular triplex (H*-DNA) formed by the d(C)37 d(G)37 insert in supercoiled plasmid in the presence of Mg2+ ions.
我们研究了一种质子化的嘧啶 - 嘌呤 - 嘌呤（Py - Pu - Pu）三链体，它在d（C）n d（G）n双链体与作为第三链的d（AG）m寡核苷酸之间形成，并带有CGA +质子化碱基三联体。我们在pH4.0、200 mM Na +且无二价阳离子的条件下，观察到携带d（C）18 d（G）18插入片段的质粒与d（AG）5寡核苷酸之间形成了这样一种分子间复合物。二价阳离子可进一步稳定该复合物。我们提出了近乎同晶型的碱基三联体TAA、CGG和CGA +的结构。为了鉴定类似H - DNA的结构，其中包括d（C）n d（G）n双链体与AG链之间的三链体，我们在超螺旋质粒中克隆了插入片段：G10TTAA（AG）5。光足迹分析以及焦碳酸二乙酯、高锰酸钾和硫酸二甲酯化学修饰的数据表明，带有CGG和CGA +碱基三联体的三链体类似H结构实际上是在酸性条件下形成的。在这项研究过程中，我们在用硫酸二甲酯（DMS）探测Py - Pu - Pu三链体时遇到了意外结果：不仅进入双链体的鸟嘌呤有保护作用，位于大沟中的第三链中的鸟嘌呤也有保护作用。我们不仅在新型质子化Py - Pu - Pu三链体的情况下证明了这种效应，而且在存在Mg2 +离子的超螺旋质粒中由d（C）37 d（G）37插入片段形成的传统非质子化Py - Pu - Pu分子内三链体（H* - DNA）的情况下也证明了这种效应。
