Presently there is great interest in the construction of nanostructures from DNA fragments.Here we report the preparation of much larger helical textures with different shapes from pure DNA fragments.We have observed them while preparing crystals of the dodecamer d(AAAAAATTTTTT),which only contains adenine and thymine.Noncoding regions of the genome are always rich in these two bases.We have found a strong influence of ions either monovalent or divalent,with which different crystalline structures are found.All of them contain long helical stacks of duplexes in the unit cell.The most remarkable structures are macroscopic helices with diameters and pitch in the range of 20-40 mum.Thus,pure DNA oligonucleotides may form a hierarchy of helical structures,going from the B-form double helix(pitch,p = 33 A)to helical stacks of duplexes(p ≈ 900 A),and to macroscopic helices(p ≈ 300,000 A).These different levels of organization are reminiscent of the different levels of organization of DNA in eukaryotic chromosomes.
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机译：目前，人们对从DNA片段构建纳米结构非常感兴趣。在这里，我们报道了从纯DNA片段制备具有不同形状的更大螺旋纹理的过程。我们在制备十二聚体d（AAAAAATTTTTT）的晶体时观察到它们，其中仅包含腺嘌呤和胸腺嘧啶。基因组的非编码区总是富含这两个碱基。我们发现一价或二价离子的强烈影响，发现它们具有不同的晶体结构。它们都在单元中包含长螺旋状双链体最显着的结构是宏观螺旋，其直径和螺距在20-40微米范围内。因此，纯净的DNA寡核苷酸可能会形成螺旋结构的层次结构，来自B型双螺旋（螺距，p = 33 A ）到双螺旋的螺旋堆叠（p≈900 A）和宏观螺旋（p≈300,000 A）。这些不同的组织水平让人联想到e中DNA的不同组织水平。真核染色体。
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