Downes C S, Clarke D J, Mullinger A M, Giménez-Abián J F, Creighton A M, Johnson R T
Department of Zoology, University of Cambridge, UK.
Nature. 1994 Dec 1;372(6505):467-70. doi: 10.1038/372467a0.
The enzyme DNA topoisomerase II, which removes the catenations formed between the DNA molecules of sister chromatids during replication and is a structural component of chromosome cores, is needed for chromosome condensation in yeast and in Xenopus extracts. Inhibitors of topoisomerase II arrest mammalian cells before mitosis in the G2 phase of the cell cycle, but also produce DNA damage, which causes arrest through established checkpoint controls. It is open to question whether cells need topoisomerase II to leave G2, or control late-cycle progression in response to its activity. Bisdioxopiperazines are topoisomerase II inhibitors that act without producing direct DNA damage; the most potent, ICRF-193, blocks mammalian entry into but not exit from mitosis. Here we show that checkpoint-evading agents such as caffeine override this block to produce abortively condensed chromosomes, indicating that topoisomerase II is needed for complete condensation. We find that exit from G2 is regulated by a catenation-sensitive checkpoint mechanism which is distinct from the G2-damage checkpoint.
DNA拓扑异构酶II在酵母和非洲爪蟾提取物中参与染色体凝聚过程，该酶在复制过程中负责去除姐妹染色单体DNA分子之间形成的连环结构，并且是染色体核心的结构组成部分。拓扑异构酶II抑制剂可使哺乳动物细胞在细胞周期的G2期有丝分裂前停滞，但同时也会造成DNA损伤，进而通过既定的检查点控制机制导致细胞停滞。细胞离开G2期是否需要拓扑异构酶II，或者是否通过对其活性的响应来控制细胞周期后期进程，这仍存在疑问。双二氧哌嗪类化合物是拓扑异构酶II抑制剂，其作用方式不会产生直接的DNA损伤；其中最有效的ICRF-193可阻止哺乳动物细胞进入有丝分裂，但不会阻止其退出有丝分裂。我们在此表明，咖啡因等逃避检查点的试剂可克服这种阻滞，产生异常凝聚的染色体，这表明完全凝聚需要拓扑异构酶II。我们发现，G2期的退出受一种连环敏感性检查点机制调控，该机制不同于G2期损伤检查点。
