Dasso M, Newport J W
Department of Biology, University of California, San Diego, La Jolla 92093.
Cell. 1990 Jun 1;61(5):811-23. doi: 10.1016/0092-8674(90)90191-g.
During cell division complete DNA replication must occur before mitosis is initiated. Using a cell-free extract derived from Xenopus eggs that oscillates between S phase and mitosis, we have investigated how completion of DNA synthesis is coupled to the initiation of mitosis. We find that Xenopus eggs contain a feedback pathway which suppresses mitosis until replication is completed and that activation of this inhibitory system is dependent on the presence of a threshold concentration of unreplicated DNA. We demonstrate that in the presence of unreplicated DNA the active feedback system inhibits initiation of mitosis by blocking the activation of MPF, a regulator of mitosis found in all eukaryotic cells. Our results demonstrate that the feedback system does not inhibit MPF activation by blocking the synthesis or accumulation of cyclin protein, a subunit of MPF, or by blocking association of cyclin with the cdc2 subunit of MPF. We propose that the feedback system blocks mitosis by maintaining MPF in an inactive state by modulating posttranslational modifications critical for MPF activation.
在细胞分裂过程中，完整的DNA复制必须在有丝分裂开始之前完成。我们使用从非洲爪蟾卵中提取的无细胞提取物，该提取物在S期和有丝分裂之间振荡，研究了DNA合成的完成是如何与有丝分裂的开始相偶联的。我们发现非洲爪蟾卵含有一种反馈途径，该途径会抑制有丝分裂，直到复制完成，并且这种抑制系统的激活取决于未复制DNA阈值浓度的存在。我们证明，在存在未复制DNA的情况下，活跃的反馈系统通过阻断MPF的激活来抑制有丝分裂的开始，MPF是一种在所有真核细胞中都存在的有丝分裂调节因子。我们的结果表明，反馈系统不会通过阻断MPF亚基细胞周期蛋白的合成或积累，或通过阻断细胞周期蛋白与MPF的cdc2亚基的结合来抑制MPF的激活。我们提出，反馈系统通过调节对MPF激活至关重要的翻译后修饰，使MPF保持在无活性状态，从而阻断有丝分裂。
