Lau P P, Gray H B, Wei C F, Legerski R J, Robberson D L
Biochim Biophys Acta. 1981 Sep 28;655(2):199-209. doi: 10.1016/0005-2787(81)90010-1.
Type I DNA topoisomerases from mouse ascites cell nuclei and from rat liver cell nuclei act on denatured viral closed circular PM2 DNA to produce molecules with a highly contracted structure as well as fully duplex non-supercoiled covalently closed circular molecules. Highly contracted DNA molecules contain a novel type of topological linkage in which a strand in one region of the double-stranded molecule passes between the strands in another region of the circular molecule one or more times. Since it is also found that the action of the topoisomerase promotes renaturation of complementary strands in denatured closed circular DNA, it is suggested that formation of contracted DNA structures proceeds through renatured, duplex intermediates with highly negative superhelix densities that contain small single-stranded regions.
来自小鼠腹水细胞核和大鼠肝细胞核的I型DNA拓扑异构酶作用于变性的病毒闭环PM2 DNA，产生具有高度收缩结构的分子以及完全双链的非超螺旋共价闭环分子。高度收缩的DNA分子包含一种新型的拓扑连接，其中双链分子一个区域中的一条链在环状分子另一个区域的链之间穿过一次或多次。由于还发现拓扑异构酶的作用促进变性闭环DNA中互补链的复性，因此有人提出收缩DNA结构的形成是通过具有高度负超螺旋密度且包含小单链区域的复性双链中间体进行的。
