Department of Molecular Biosciences, Northwestern University, Evanston, IL, 60208, USA.
Institute for Research in Immunology and Cancer, Université de Montréal, Montréal, Québec, H3C 3J7, Canada.
Sci Rep. 2017 Oct 27;7(1):14279. doi: 10.1038/s41598-017-14701-5.
Large-scale chromatin remodeling during mitosis is catalyzed by a heteropentameric enzyme known as condensin. The DNA-organizing mechanism of condensin depends on the energy of ATP hydrolysis but how this activity specifically promotes proper compaction and segregation of chromosomes during mitosis remains poorly understood. Purification of budding yeast condensin reveals that it occurs not only in the classical heteropentameric "monomer" form, but that it also adopts much larger configurations consistent with oligomerization. We use a single-DNA magnetic tweezers assay to study compaction of DNA by yeast condensin, with the result that only the multimer shows ATP-enhanced DNA-compaction. The compaction reaction involves step-like events of 200 nm (600 bp) size and is strongly suppressed by forces above 1 pN, consistent with a loop-capture mechanism for initial binding and compaction. The compaction reactions are largely insensitive to DNA torsional stress. Our results suggest a physiological role for oligomerized condensin in driving gradual chromatin compaction by step-like and slow "creeping" dynamics consistent with a loop-extrusion mechanism.
在有丝分裂过程中，大规模的染色质重塑是由一种称为凝聚酶的异五聚体酶催化的。凝聚酶的 DNA 组织机制依赖于 ATP 水解的能量，但这种活性如何特异性地促进有丝分裂过程中染色体的适当压缩和分离，仍知之甚少。芽殖酵母凝聚酶的纯化表明，它不仅以经典的异五聚体“单体”形式存在，而且还采用了与寡聚化一致的更大构象。我们使用单 DNA 磁镊测定法研究酵母凝聚酶对 DNA 的压缩，结果表明只有多聚体显示出 ATP 增强的 DNA 压缩。压缩反应涉及 200nm（600bp）大小的分步事件，并且在超过 1pN 的力下被强烈抑制，与初始结合和压缩的环捕获机制一致。压缩反应对 DNA 扭结张力的敏感性不大。我们的结果表明，寡聚凝聚酶在通过类似于环挤出机制的分步和缓慢“爬行”动力学驱动逐渐染色质压缩方面具有生理作用。
