Marx K A, Ruben G C
Nucleic Acids Res. 1983 Mar 25;11(6):1839-54. doi: 10.1093/nar/11.6.1839.
In spermidine-condensed calf thymus DNA preparations, torus-shaped condensates were shown by transmission electron microscopy to exist under the hydrated conditions of the freeze fracture experiment. Using extremely low Pt metal deposition levels (9 A Pt/C) high-contrast replicas of the spermidine-DNA toruses were obtained that showed circumferential wrapping of single DNA double helix-size surface fibres. Stereoscopic analysis of high magnification stereomicrographs established some details of the three-dimensional organization of two DNA double helix sections winding circumferentially on the inner surface of one such torus. These measurements demonstrate the usefulness of stereoscopic analysis of these high macromolecular organization magnification. Measurements on a number of torus-shaped complexes (n = 16) yielded these average dimensions: inner circumference (1840 +/- 204 A) outer circumference (2800 +/- 222 A), torus ring thickness (143 +/- 18 A). These data support a continuous circumferential DNA-winding model of torus organization proposed by Marx & Reynolds.
在亚精胺凝聚的小牛胸腺DNA制剂中，通过透射电子显微镜发现在冷冻断裂实验的水合条件下存在环形凝聚物。使用极低的铂金属沉积水平（9 Å Pt/C），获得了亚精胺-DNA环的高对比度复制品，显示出单个DNA双螺旋大小的表面纤维的周向包裹。对高倍立体显微镜照片的立体分析确定了在一个这样的环的内表面上周向缠绕的两个DNA双螺旋部分的三维组织的一些细节。这些测量证明了对这些高分子组织放大倍数进行立体分析的有用性。对许多环形复合物（n = 16）的测量得出了这些平均尺寸：内周长（1840 +/- 204 Å）、外周长（2800 +/- 222 Å）、环厚度（143 +/- 18 Å）。这些数据支持了马克思和雷诺兹提出的环组织的连续周向DNA缠绕模型。
