Reich Z, Levin-Zaidman S, Gutman S B, Arad T, Minsky A
Department of Organic Chemistry, Weizmann Institute of Science, Rehovot, Israel.
Biochemistry. 1994 Nov 29;33(47):14177-84. doi: 10.1021/bi00251a029.
Electron microscopy and circular dichroism studies of cholesteric aggregates derived from topologically-constrained DNA molecules indicate that the overall morphology and structural properties of these aggregates are fundamentally different from those characterizing condensed structures of nonconstrained DNA species. Specifically, the cholesteric pitch and twist of all hitherto characterized lyotropic mesophases of biopolymers--including those obtained from linear DNA--depend predominantly upon environmental parameters such as the dielectric constant of the solvent. In contrast, the properties of aggregates derived from closed circular supercoiled DNA are found to be solely and directly dictated by the superhelical density and handedness. On the basis of these results, as well as on the demonstrated ubiquity of liquid-crystalline DNA organizations in vivo, we suggest that supercoiling-regulated liquid crystallinity represents an effective packaging mode of nucleosome-free, topologically-constrained DNA molecules in living systems.
对源自拓扑受限DNA分子的胆甾相聚集体进行的电子显微镜和圆二色性研究表明，这些聚集体的整体形态和结构性质与非受限DNA物种凝聚结构的特征有着根本的不同。具体而言，所有迄今已表征的生物聚合物溶致液晶相——包括从线性DNA获得的那些——的胆甾螺距和扭曲主要取决于环境参数，如溶剂的介电常数。相比之下，发现源自闭环超螺旋DNA的聚集体的性质完全且直接由超螺旋密度和螺旋方向决定。基于这些结果，以及体内液晶DNA组织已被证明的普遍性，我们认为超螺旋调节的液晶性代表了活系统中无核小体、拓扑受限DNA分子的一种有效包装模式。
