Chromosome Dynamics Laboratory, RIKEN, 2-1 Hirosawa, Wako, Saitama 351-0198, Japan.
Institute of Industrial Sciences, The University of Tokyo, 4-6-1 Komaba, Meguro-ku, Tokyo 153-8505, Japan.
Dev Cell. 2015 Apr 6;33(1):94-106. doi: 10.1016/j.devcel.2015.01.034.
Condensin I is a five-subunit protein complex that plays a central role in mitotic chromosome assembly and segregation in eukaryotes. To dissect its mechanism of action, we reconstituted wild-type and mutant complexes from recombinant subunits and tested their abilities to assemble chromosomes in Xenopus egg cell-free extracts depleted of endogenous condensins. We find that ATP binding and hydrolysis by SMC subunits have distinct contributions to the action of condensin I and that continuous ATP hydrolysis is required for structural maintenance of chromosomes. Mutant complexes lacking either one of two HEAT subunits produce abnormal chromosomes with highly characteristic defects and have contrasting structural effects on chromosome axes preassembled with the wild-type complex. We propose that balancing acts of the two HEAT subunits support dynamic assembly of chromosome axes under the control of the SMC ATPase cycle, thereby governing construction of rod-shaped chromosomes in eukaryotic cells.
凝缩素 I 是由五个亚基组成的蛋白复合物，在真核生物有丝分裂染色体的组装和分离中起着核心作用。为了剖析其作用机制，我们使用重组亚基重新组成野生型和突变型复合物，并在耗尽内源性凝缩素的非洲爪蟾卵无细胞提取物中测试它们组装染色体的能力。我们发现 SMC 亚基的 ATP 结合和水解对凝缩素 I 的作用有不同的贡献，并且连续的 ATP 水解对于染色体结构的维持是必需的。缺乏两个 HEAT 亚基之一的突变型复合物产生具有高度特征性缺陷的异常染色体，并且对与野生型复合物预先组装的染色体轴具有相反的结构影响。我们提出，两个 HEAT 亚基的平衡作用支持在 SMC ATP 酶循环的控制下染色体轴的动态组装，从而控制真核细胞中杆状染色体的构建。
