科學(xué)家發(fā)現(xiàn)了當(dāng)雙鏈DNA拉伸超過了其極限的時候會熔化破碎，就仿佛遇到了高溫,。這些結(jié)果可能為理解DNA-蛋白質(zhì)的相互作用以及DNA的熱動力學(xué)——它們對于包括細(xì)胞分裂和轉(zhuǎn)錄在內(nèi)的一些細(xì)胞過程至關(guān)重要——提供一個基礎(chǔ),。
Erwin Peterman及其同事“過度拉伸”了這種核酸螺旋,，把每一個分子鏈的一端與一個固體微球相連接，從而研究了DNA的彈性,。這組科學(xué)家指出,，拉伸最初可能始于腺嘌呤和胸腺嘧啶豐富的區(qū)域，而且雙鏈DNA需要一個最低程度的力量才能開始分解,。這種過分拉伸始于末端的綻裂,，而且一直向兩個方向運動，直到這些螺旋狀損傷的DNA鏈破碎形成單鏈,。這組作者說,，然而，當(dāng)DNA的兩條鏈都固定于一個固態(tài)基底的時候,，熔化這些鏈所需的力量幾乎加倍了,。（生物谷Bioon.com）
生物谷推薦原始出處：
PNAS October 19, 2009, doi: 10.1073/pnas.0904322106
Unraveling the structure of DNA during overstretching by using multicolor, single-molecule fluorescence imaging
Joost van Mamerena,1,2, Peter Grossa,1, Geraldine Fargea, Pleuni Hooijmana, Mauro Modestib, Maria Falkenbergc, Gijs J. L. Wuitea,1,3,4 and Erwin J. G. Petermana,1,3,4
aDepartment of Physics and Astronomy and Laser Centre, Vrije Universiteit, De Boelelaan 1081, 1081 HV, Amsterdam, The Netherlands;
bCentre National de la Recherche Scientifique, Unité Propre de Recherche 3081, Genome Instability and Carcinogenesis Conventionné par l'Université d'Aix-Marseille 2, 13402 Marseille Cedex 20, France; and
cDepartment of Medical Biochemistry and Cell Biology, G?teborg University, Box 440 SE-40530 G?teborg, Sweden
Single-molecule manipulation studies have revealed that double-stranded DNA undergoes a structural transition when subjected to tension. At forces that depend on the attachment geometry of the DNA (65 pN or 110 pN), it elongates ≈1.7-fold and its elastic properties change dramatically. The nature of this overstretched DNA has been under debate. In one model, the DNA cooperatively unwinds, while base pairing remains intact. In a competing model, the hydrogen bonds between base pairs break and two single DNA strands are formed, comparable to thermal DNA melting. Here, we resolve the structural basis of DNA overstretching using a combination of fluorescence microscopy, optical tweezers, and microfluidics. In DNA molecules undergoing the transition, we visualize double- and single-stranded segments using specific fluorescent labels. Our data directly demonstrate that overstretching comprises a gradual conversion from double-stranded to single-stranded DNA, irrespective of the attachment geometry. We found that these conversions favorably initiate from nicks or free DNA ends. These discontinuities in the phosphodiester backbone serve as energetically favorable nucleation points for melting. When both DNA strands are intact and no nicks or free ends are present, the overstretching force increases from 65 to 110 pN and melting initiates throughout the molecule, comparable to thermal melting. These results provide unique insights in the thermodynamics of DNA and DNA-protein interactions.
