Parrack P K, Datta S, Sasisekharan V
Molecular Biophysics Unit, Indian Institute of Science, Bangalore.
J Biomol Struct Dyn. 1984 Aug;2(1):149-57. doi: 10.1080/07391102.1984.10507553.
A thorough investigation of salt concentration dependence of lithium DNA fibres is made using X-ray diffraction. While for low salt the C-form pattern is obtained, crystalline B-type diffraction patterns result on increasing the salt concentration. The salt content in the gel (from which fibres are drawn) is estimated by equilibrium dialysis using the Donnan equilibrium principle. The salt range giving the best crystalline B pattern is determined. It is found that in this range meridional reflections occur on the fourth and sixth layer lines. In addition, the tenth layer meridian is absent at a particular salt concentration. These results strongly suggest the presence of non-helical features in the DNA molecule. Preliminary analysis of the diffraction patterns indicates a structural variability within the B-form itself. Further, the possibility of the structural parameters of DNA being similar in solid state and in solution is discussed.
利用X射线衍射对锂-DNA纤维的盐浓度依赖性进行了全面研究。在低盐浓度下可获得C型图案，而随着盐浓度的增加则会产生结晶B型衍射图案。使用唐南平衡原理通过平衡透析法估算了（从中抽取纤维的）凝胶中的盐含量。确定了产生最佳结晶B型图案的盐浓度范围。发现在该范围内，第四层线和第六层线上出现了子午线反射。此外，在特定盐浓度下第十层子午线不存在。这些结果有力地表明DNA分子中存在非螺旋特征。对衍射图案的初步分析表明B型结构本身存在结构变异性。此外，还讨论了DNA在固态和溶液中结构参数相似的可能性。
