Downing K H
Ultramicroscopy. 1984;13(1-2):35-46. doi: 10.1016/0304-3991(84)90055-x.
The conformation of DNA in thin, platelet crystals is being studied by electron microscopy and diffraction, and by other techniques including circular dichroism spectroscopy. Specimens are prepared in the frozen-hydrated state for the electron microscope. Electron diffraction patterns from the crystals extend to 3.5 A, and lattice images with resolution to 6.5 A have been obtained. Electron diffraction patterns from fibers in the same preparations show a stacking distance between base pairs which is larger than in most DNA conformations. The data so far available can be interpreted to indicate that the DNA in the crystals is in a conformation which has not previously been reported and which is in the B family, unwound to have 12 base pairs per turn. Model calculations have been performed which support this interpretation and which show that a three-dimensional reconstruction, with even very limited data, could confirm the helix parameters.
目前正在通过电子显微镜、衍射以及包括圆二色光谱在内的其他技术来研究薄片状血小板晶体中DNA的构象。样本以冷冻水合状态制备用于电子显微镜观察。晶体的电子衍射图谱可延伸至3.5埃，并且已经获得了分辨率达6.5埃的晶格图像。来自相同制备物中纤维的电子衍射图谱显示，碱基对之间的堆积距离比大多数DNA构象中的要大。目前可得的数据可以解释为表明晶体中的DNA处于一种先前未被报道过的构象，且属于B型家族，每圈展开有12个碱基对。已经进行了模型计算，这些计算支持了这一解释，并表明即使数据非常有限，三维重建也能够确认螺旋参数。
