Eukaryotes carry three types of structural maintenance of chromosome (SMC) protein complexes, condensin, cohesin, and SMC5/6, which are ATP-dependent motor proteins that remodel the genome via DNA loop extrusion (LE). SMCs modulate DNA supercoiling but remains incompletely understood how this is achieved. Using a single-molecule magnetic tweezers assay that directly measures how much twist is induced by individual SMCs in each LE step, we demonstrate that all three SMC complexes induce the same large negative twist (i.e., linking number change Δ L k of ~−0.6 at each LE step) into the extruded loop, independent of step size and DNA tension. Using ATP hydrolysis mutants and nonhydrolyzable ATP analogs, we find that ATP binding is the twist-inducing event during the ATPase cycle, coinciding with the force-generating LE step. The fact that all three eukaryotic SMC proteins induce the same amount of twist indicates a common DNA-LE mechanism among these SMC complexes.

中文翻译：

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所有真核 SMC 蛋白在每个 DNA 环挤出步骤中诱导 -0.6 的扭曲


真核生物携带三种类型的染色体结构维持 （SMC） 蛋白复合物，即凝聚素、黏连蛋白和 SMC5/6，它们是 ATP 依赖性运动蛋白，可通过 DNA 环挤出 （LE） 重塑基因组。SMC 调节 DNA 超螺旋，但尚不完全清楚这是如何实现的。使用直接测量每个 LE 步骤中单个 SMC 诱导多少扭曲的单分子磁镊测定法，我们证明所有三种 SMC 复合物都诱导相同的大负扭曲（即，每个 LE 步骤的连接数变化 Δ L k 为 ~-0.6）到挤出环中，与步长和 DNA 张力无关。使用 ATP 水解突变体和不可水解的 ATP 类似物，我们发现 ATP 结合是 ATP 酶循环期间的扭曲诱导事件，与产生力的 LE 步骤相吻合。所有三种真核 SMC 蛋白诱导相同数量的扭曲这一事实表明这些 SMC 复合物之间存在共同的 DNA-LE 机制。