Schutte B C, Cox M M
Department of Biochemistry, College of Agricultural and Life Sciences, University of Wisconsin--Madison 53706.
Biochemistry. 1988 Oct 4;27(20):7886-94. doi: 10.1021/bi00420a046.
RecA protein promoted formation of paranemic joints, in which a recA-ssDNA complex and a nicked circular dsDNA molecule are homologously aligned without net cross-strand interwinding, is accompanied by extensive underwinding of the dsDNA molecule. When the nick is sealed by DNA ligase, a highly negatively superhelical DNA molecule is formed. This underwinding has the following properties: (a) it occurs within 2 min; (b) it is completely homology dependent; (c) it does not require a homologous free DNA end. The resulting underwound DNA species is comprised of a heterogeneous population of topoisomers. The degree of unwinding exhibits a strong dependence on the fractional length of homology in the dsDNA molecule and indicates that paranemic joints can extend for at least 2900 base pairs. The rapid underwinding associated with paranemic joint formation is followed by a longer phase in which the dsDNA molecule is more extensively underwound.
RecA蛋白促进了平行双链节的形成，其中recA-单链DNA复合物与带切口的环状双链DNA分子同源排列，没有净交叉链缠绕，同时双链DNA分子会发生广泛的解旋。当切口被DNA连接酶封闭时，会形成高度负超螺旋的DNA分子。这种解旋具有以下特性：（a）在2分钟内发生；（b）完全依赖同源性；（c）不需要同源游离DNA末端。产生的解旋DNA种类由拓扑异构体的异质群体组成。解旋程度对双链DNA分子中同源性的分数长度有很强的依赖性，表明平行双链节可以延伸至少2900个碱基对。与平行双链节形成相关的快速解旋之后是一个更长的阶段，在此阶段双链DNA分子的解旋更为广泛。
