中文摘要：

DNA拓扑异构酶与断开DNA链和改变其拓扑结构有关。先前的研究认为，拓扑异构酶Type ⅡB 是由Type ⅡA通过基因的复制、重组和缺失所造成。然而，本研究结果则显示，TypeⅠA与TypeⅡB的进化关系较近，而TypeⅡA与TypeⅡB的关系较远。因此，TypeⅡB可能是由TypeⅠA演化而来，或者说，TypeⅡB是TypeⅠA在古细菌中的特化形式；TypeⅡB可能是由TypeⅡA通过形成TypeⅠA后演化而成的，而不是由TypeⅡA直接通过基因的复制、重组和缺失所造成。在由TypeⅡA演化成为TypeⅠA，最后演化为TypeⅡB的过程中，DNA拓扑异构酶的催化机制也发生了变化：从需要金属离子的协助，演化到了不需要镁离子的存在协助其催化。

英文摘要：

DNA strand scission and topology changes are catalyzed by DNA topoisomerases. Previous studies suggest that Type ⅡB topoisomerase evolved from Type Ⅱ A by gene duplication, recombination and absence. However, this study shows that the evolutionary relationship between TypeⅠ A and Ⅱ B is closer than that between Type Ⅱ A and ⅡB. Thus, Type Ⅱ B is possibly from Type Ⅰ A, or Type ⅡB is a special form ofⅠ A in arehaebacteria; Type Ⅱ B is probably evolved from Ⅱ A via ⅠA rather than from Ⅱ A directly. During the evolution of Ⅱ A to Ⅱ B via Ⅰ A, the catalytic mechanisms of DNA topoisomerases have also been changed ; that is, metal ions are necessary in the catalyses for beth Ⅰ A and Ⅱ A, but no ion is needed for Ⅱ B.