Salt dependence of the elasticity and overstretching transition of single DNA molecules
Salt dependence of the elasticity and overstretching transition of single DNA molecules
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DOI：
10.1016/s0006-3495(02)75658-0
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发表时间：
2002-06-01
影响因子：
3.4
通讯作者：
Bloomfield, VA
中科院分区：
文献类型：
--
作者：
Wenner, JR;Williams, MC;Bloomfield, VA
当双链DNA被拉伸到其B形轮廓长度时，聚合物弹性模型可以描述测量力的急剧增加。当分子被拉伸超过这个轮廓长度时，它显示出高度合作的过度伸展转变。我们通过在光镊仪中拉伸单个DNA分子，测量了作为单价盐浓度的函数的弹性和超拉伸跃迁。当钠离子浓度从1000 mm降低到2.57 mm时，DNA的持续长度从46 nm增加到59 nm，而弹性拉伸模数基本保持不变。这些结果与Podgomik等人的模型一致。(2000)，J.Chem.太棒了。113：9343-9350)，每次充电的有效DNA长度为0.67 nm。在相同的范围内，随着单价盐浓度的降低，超伸缩转变力从68 pN减小到52 pN。这种作用力的降低归因于DNA双螺旋的稳定性随着盐浓度的降低而降低。尽管如前所述，当DNA过度拉伸时，将DNA链保持在螺旋构象中的氢键会断裂，但这些数据表明，在过渡期间，两条DNA链保持紧密联系。
As double-stranded DNA is stretched to its B-form contour length, models of polymer elasticity can describe the dramatic increase in measured force. When the molecule is stretched beyond this contour length, it shows a highly cooperative overstretching transition. We have measured the elasticity and overstretching transition as a function of monovalent salt concentration by stretching single DNA molecules in an optical tweezers apparatus. As the sodium ion concentration was decreased from 1000 to 2.57 mM, the persistence length of DNA increased from 46 to 59 nm, while the elastic stretch modulus remained approximately constant. These results are consistent with the model of Podgomik et al. (2000, J. Chem. Phys. 113:9343-9350) using an effective DNA length per charge of 0.67 nm. As the monovalent salt concentration was decreased over the same range, the overstretching transition force decreased from 68 to 52 pN. This reduction in force is attributed to a decrease in the stability of the DNA double helix with decreasing salt concentration. Although, as was shown previously, the hydrogen bonds holding DNA strands in a helical conformation break as DNA is overstretched, these data indicate that both DNA strands remain close together during the transition.