Wang Xindan, Brandão Hugo B, Le Tung B K, Laub Michael T, Rudner David Z
Department of Microbiology and Immunobiology, Harvard Medical School, 77 Avenue Louis Pasteur, Boston, MA 02115, USA.
Graduate Program in Biophysics, Harvard University, Cambridge, MA 02138, USA.
Science. 2017 Feb 3;355(6324):524-527. doi: 10.1126/science.aai8982.
Structural maintenance of chromosomes (SMC) complexes play critical roles in chromosome dynamics in virtually all organisms, but how they function remains poorly understood. In the bacterium Bacillus subtilis, SMC-condensin complexes are topologically loaded at centromeric sites adjacent to the replication origin. Here we provide evidence that these ring-shaped assemblies tether the left and right chromosome arms together while traveling from the origin to the terminus (>2 megabases) at rates >50 kilobases per minute. Condensin movement scales linearly with time, providing evidence for an active transport mechanism. These data support a model in which SMC complexes function by processively enlarging DNA loops. Loop formation followed by processive enlargement provides a mechanism by which condensin complexes compact and resolve sister chromatids in mitosis and by which cohesin generates topologically associating domains during interphase.
染色体结构维持（SMC）复合物在几乎所有生物体的染色体动态变化中都起着关键作用，但其作用机制仍知之甚少。在枯草芽孢杆菌中，SMC-凝聚素复合物在与复制起点相邻的着丝粒位点进行拓扑加载。在此，我们提供证据表明，这些环状组装体在以每分钟超过50千碱基的速度从起点向终点（超过2兆碱基）移动时，将左右染色体臂拴在一起。凝聚素的移动与时间呈线性关系，这为一种主动运输机制提供了证据。这些数据支持了一个模型，即SMC复合物通过逐步扩大DNA环来发挥作用。环的形成随后进行逐步扩大，提供了一种机制，通过该机制凝聚素复合物在有丝分裂中压缩并分离姐妹染色单体，以及黏连蛋白在间期产生拓扑相关结构域。
