Van Meervelt L, Vlieghe D, Dautant A, Gallois B, Précigoux G, Kennard O
Department of Chemistry, Katholieke Universiteit Leuven, Heverlee, Belgium.
Nature. 1995 Apr 20;374(6524):742-4. doi: 10.1038/374742a0.
Triple helices result from interaction between single- and double-stranded nucleic acids. Their formation is a possible mechanism for recombination of homologous gene sequences in nature and provides, inter alia, a basis for artificial control of gene activity. Triple-helix motifs have been extensively studied by a variety of techniques, but few high-resolution structural data are available. The only triplet structures characterized so far by X-ray diffraction were in protein-DNA complexes studied at about 3 A resolution. We report here the X-ray analysis of a DNA nonamer, d(GCGAATTCG), to a resolution of 2.05 A, in which the extended crystal structure contains (C.G)*G triplets as a fragment of triple helix. The guanosine-containing chains are in a parallel orientation. This arrangement is a necessary feature of models for homologous recombination which results ultimately in replacement of one length of DNA by another of similar sequence. The present-structure agrees with many published predictions of triplex organization, and provides an accurate representation of an element that allows sequence-specific association between single- and double-stranded nucleic acids.
三链螺旋是由单链和双链核酸之间的相互作用产生的。它们的形成是自然界中同源基因序列重组的一种可能机制，尤其为基因活性的人工控制提供了基础。三链螺旋基序已通过多种技术进行了广泛研究，但可用的高分辨率结构数据很少。迄今为止，唯一通过X射线衍射表征的三联体结构是在约3埃分辨率下研究的蛋白质-DNA复合物中。我们在此报告了一个DNA九聚体d(GCGAATTCG)的X射线分析，分辨率为2.05埃，其中扩展晶体结构包含(C.G)*G三联体作为三链螺旋的一个片段。含鸟苷的链呈平行取向。这种排列是同源重组模型的一个必要特征，同源重组最终导致一段DNA被另一段相似序列的DNA所取代。目前的结构与许多已发表的三链体组织预测一致，并提供了一个能准确呈现允许单链和双链核酸之间进行序列特异性结合的元件的结构。
