Human topoisomerase IIα rapidly relaxes positively supercoiled DNA -: Implications for enzyme action ahead of replication forks
Human topoisomerase IIα rapidly relaxes positively supercoiled DNA -: Implications for enzyme action ahead of replication forks
复制标题
DOI：
10.1074/jbc.m503320200
复制
发表时间：
2005-11-25
影响因子：
4.8
通讯作者：
Osheroff, N
中科院分区：
文献类型：
--
作者：
McClendon, AK;Rodriguez, AC;Osheroff, N
DNA复制机器通过双螺旋的运动诱导了叉前的急性正超螺旋和叉后的precatenanes。由于拓扑异构酶I和II分别产生短暂的单链和双链DNA断裂，因此人们认为I型酶松弛了复制叉前的正超螺旋。相反，II型酶主要分解前环烷烃并解开连锁的子染色体。然而，对酵母和细菌的研究表明，II型拓扑异构酶也可能在复制机制之前发挥作用。如果是这样的话，那么阳性DNA超螺旋应该是拓扑异构酶II α的首选松弛底物，拓扑异构酶II α是人类复制过程中涉及的酶亚型。结果表明，人拓扑异构酶II α松弛正超螺旋质粒比负超螺旋分子快> 10倍。相反，DNA复制不需要的拓扑异构酶II β则没有这种偏好。除了其高松弛速率之外，拓扑异构酶II α与正超螺旋分子保持较低水平的DNA切割复合物。这些特性表明，人拓扑异构酶II α有可能以有效且安全的方式减轻复制叉之前的扭转应力。
Movement of the DNA replication machinery through the double helix induces acute positive supercoiling ahead of the fork and precatenanes behind it. Because topoisomerase I and II create transient single- and double-stranded DNA breaks, respectively, it has been assumed that type I enzymes relax the positive supercoils that precede the replication fork. Conversely, type II enzymes primarily resolve the precatenanes and untangle catenated daughter chromosomes. However, studies on yeast and bacteria suggest that type II topoisomerases may also function ahead of the replication machinery. If this is the case, then positive DNA supercoils should be the preferred relaxation substrate for topoisomerase II alpha, the enzyme isoform involved in replicative processes in humans. Results indicate that human topoisomerase II alpha relaxes positively supercoiled plasmids > 10-fold faster than negatively supercoiled molecules. In contrast, topoisomerase II beta, which is not required for DNA replication, displays no such preference. In addition to its high rates of relaxation, topoisomerase II alpha maintains lower levels of DNA cleavage complexes with positively supercoiled molecules. These properties suggest that human topoisomerase II alpha has the potential to alleviate torsional stress ahead of replication forks in an efficient and safe manner.