Voloshin O N, Mirkin S M, Lyamichev V I, Belotserkovskii B P, Frank-Kamenetskii M D
Institute of Molecular Genetics, USSR Academy of Sciences, Moscow.
Nature. 1988 Jun 2;333(6172):475-6. doi: 10.1038/333475a0.
We have recently shown that under superhelical stress and/or acid pH the homopurine-homopyrimidine tracts conforming to the mirror symmetry (H palindromes) form a novel DNA structure, the H form. According to our model, the H form includes (1) a triplex formed by half of the purine strand and by the homopyrimidine hairpin and (2) the unstructured other half of the purine strand. We used four specially designed sequences to demonstrate that, in accordance with our model, the mirror symmetry is essential for facile formation of the H form detected by two-dimensional gel electrophoresis. Here we report that, under conditions favouring the H-form extrusion, guanines of the 3' half of the purine strand are protected against alkylation by dimethylsulphate, whereas adenines of the 5' half of the purine strand react with diethyl pyrocarbonate. These data indicate that the 3' half of the homopurine strand is within the triplex whereas the 5' half is unstructured, in full agreement with our model.
我们最近发现，在超螺旋应力和/或酸性pH条件下，符合镜像对称的同型嘌呤-同型嘧啶序列（H回文序列）会形成一种新型DNA结构，即H型。根据我们的模型，H型包括：（1）由一半嘌呤链和同型嘧啶发夹形成的三链体，以及（2）嘌呤链的另一半无结构部分。我们使用了四个特别设计的序列来证明，根据我们的模型，镜像对称对于通过二维凝胶电泳检测到的H型的轻松形成至关重要。在此我们报告，在有利于H型挤出的条件下，嘌呤链3'端一半的鸟嘌呤受到硫酸二甲酯的烷基化保护，而嘌呤链5'端一半的腺嘌呤则与焦碳酸二乙酯发生反应。这些数据表明，同型嘌呤链的3'端一半位于三链体内，而5'端一半是无结构的，这与我们的模型完全一致。
