Allemand J F, Bensimon D, Lavery R, Croquette V
Laboratoire de Physique Statistique, Ecole Normale Supérieure, Unité de Recherche Associée D 1306 Centre National de la Recherche Scientifique, Paris Cedex 05,
Proc Natl Acad Sci U S A. 1998 Nov 24;95(24):14152-7. doi: 10.1073/pnas.95.24.14152.
We investigate structural transitions within a single stretched and supercoiled DNA molecule. With negative supercoiling, for a stretching force >0.3 pN, we observe the coexistence of B-DNA and denatured DNA from sigma approximately -0.015 down to sigma = -1. Surprisingly, for positively supercoiled DNA (sigma > +0.037) stretched by 3 pN, we observe a similar coexistence of B-DNA and a new, highly twisted structure. Experimental data and molecular modeling suggest that this structure has approximately 2.62 bases per turn and an extension 75% larger than B-DNA. This structure has tightly interwound phosphate backbones and exposed bases in common with Pauling's early DNA structure [Pauling, L. & Corey, R. B. (1953), Proc. Natl. Acad. Sci. USA 39, 84-97] and an unusual structure proposed for the Pf1 bacteriophage [Liu, D. J. & Day, L. A. (1994) Science 265, 671-674].
我们研究了单个拉伸和超螺旋DNA分子内的结构转变。对于负超螺旋，当拉伸力>0.3 pN时，我们观察到从σ约-0.015到σ = -1，B-DNA和变性DNA共存。令人惊讶的是，对于被3 pN拉伸的正超螺旋DNA（σ > +0.037），我们观察到B-DNA与一种新的高度扭曲结构类似的共存情况。实验数据和分子模型表明，这种结构每圈约有2.62个碱基，其伸展比B-DNA大75%。这种结构具有紧密缠绕的磷酸骨架和暴露的碱基，这与鲍林早期的DNA结构[鲍林，L. 和科里，R. B.（1953年），《美国国家科学院院刊》39，84 - 97]以及为Pf1噬菌体提出的一种不寻常结构[刘，D. J. 和戴，L. A.（1994年）《科学》265，671 - 674]相同。
