Department of Physics and Astronomy and LaserLaB Amsterdam, Vrije Universiteit Amsterdam, De Boelelaan 1081, 1081 HV Amsterdam, The Netherlands.
Nat Commun. 2016 Jun 6;7:11810. doi: 10.1038/ncomms11810.
Regions of the genome are often held under torsional constraint. Nevertheless, the influence of such constraint on DNA-protein interactions during genome metabolism is still poorly understood. Here using a combined optical tweezers and fluorescence microscope, we quantify and explain how torsional constraint influences the structural stability of DNA under applied tension. We provide direct evidence that concomitant basepair melting and helical unwinding can occur in torsionally constrained DNA at forces >∼50 pN. This striking result indicates that local changes in linking number can be absorbed by the rest of the DNA duplex. We also present compelling new evidence that an overwound DNA structure (likely P-DNA) is created (alongside underwound structures) at forces >∼110 pN. These findings substantiate previous theoretical predictions and highlight a remarkable structural plasticity of torsionally constrained DNA. Such plasticity may be required in vivo to absorb local changes in linking number in DNA held under torsional constraint.
基因组的某些区域经常受到扭转约束。然而，这种约束对基因组代谢过程中 DNA-蛋白质相互作用的影响仍知之甚少。在这里，我们使用光镊和荧光显微镜的组合，定量并解释了扭转约束如何影响拉伸下 DNA 的结构稳定性。我们提供了直接的证据表明，在扭转约束的 DNA 中，伴随着碱基对的熔解和螺旋的展开，可以在力 >∼50 pN 下发生。这一惊人的结果表明，局部的连接数变化可以被 DNA 双螺旋的其余部分吸收。我们还提供了令人信服的新证据，表明在力 >∼110 pN 下会产生超螺旋的 DNA 结构（可能是 P-DNA）（以及欠旋结构）。这些发现证实了以前的理论预测，并强调了扭转约束 DNA 的显著结构可塑性。这种可塑性可能是在体内吸收扭转约束下 DNA 中局部连接数变化所必需的。
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