Danilowicz Claudia, Limouse Charles, Hatch Kristi, Conover Alyson, Coljee Vincent W, Kleckner Nancy, Prentiss Mara
Department of Physics, Harvard University, Cambridge, MA 02138, USA.
Proc Natl Acad Sci U S A. 2009 Aug 11;106(32):13196-201. doi: 10.1073/pnas.0904729106. Epub 2009 Jul 28.
It has been suggested that the structure that results when double-stranded DNA (dsDNA) is pulled from the 3'3' ends differs from that which results when it is pulled from the 5'5' ends. In this work, we demonstrate, using lambda phage dsDNA, that the overstretched states do indeed show different properties, suggesting that they correspond to different structures. For 3'3' pulling versus 5'5' pulling, the following differences are observed: (i) the forces at which half of the molecules in the ensemble have made a complete force-induced transition to single stranded DNA are 141 +/- 3 pN and 122 +/- 4 pN, respectively; (ii) the extension vs. force curve for overstretched DNA has a marked change in slope at 127 +/- 3 pN for 3'3' and 110 +/- 3 pN for 5'5'; (iii) the hysteresis (H) in the extension vs. force curves at 150 mM NaCl is 0.3 +/- 0.8 pN microm for 3'3' versus 13 +/- 8 pN for 5'5'; and (iv) 3'3' and 5'5' molecules show different changes in hysteresis due to interactions with beta-cyclodextrin, a molecule that is known to form stable host-guest complexes with rotated base pairs, and glyoxal that is known to bind stably to unpaired bases. These differences and additional findings are well-accommodated by the corresponding structures predicted on theoretical grounds.
有人提出，当双链DNA（dsDNA）从3'3'端拉伸时所形成的结构，与从5'5'端拉伸时所形成的结构不同。在这项工作中，我们使用λ噬菌体dsDNA证明，过度拉伸状态确实表现出不同的特性，这表明它们对应于不同的结构。对于3'3'拉伸与5'5'拉伸，观察到以下差异：（i）在总体中一半分子完成力诱导向单链DNA转变时的力，分别为141±3 pN和122±4 pN；（ii）过度拉伸DNA的延伸与力曲线，对于3'3'拉伸在127±3 pN处斜率有明显变化，对于5'5'拉伸在110±3 pN处斜率有明显变化；（iii）在150 mM NaCl条件下，延伸与力曲线中的滞后现象（H），对于3'3'拉伸为0.3±0.8 pN·μm，对于5'5'拉伸为13±8 pN；（iv）3'3'和5'5'分子由于与β-环糊精（一种已知能与旋转碱基对形成稳定主客体复合物的分子）和乙二醛（一种已知能稳定结合未配对碱基的分子）相互作用，在滞后现象上表现出不同变化。这些差异和其他发现与基于理论预测的相应结构非常吻合。
