Han W, Dlakic M, Zhu Y J, Lindsay S M, Harrington R E
Department of Physics and Astronomy, Arizona State University, Tempe, AZ 85287-1504, USA.
Proc Natl Acad Sci U S A. 1997 Sep 30;94(20):10565-70. doi: 10.1073/pnas.94.20.10565.
A novel atomic force microscope with a magnetically oscillated tip has provided unprecedented resolution of small DNA fragments spontaneously adsorbed to mica and imaged in situ in the presence of divalent ions. Kinks (localized bends of average angle 78 degrees) were observed in axially strained minicircles consisting of tandemly repeated d(A)5 and d(GGGCC[C]) sequences. The frequency of kinks in identical minicircles increased 4-fold in the presence of 1 mM Zn2+ compared with 1 mM Mg2+. Kinking persisted in mixed Mg2+/Zn2+ electrolytes until the Zn2+ concentration dropped below 100 microM, indicating that this type of kinking may occur under physiological conditions. Kinking appears to replace intrinsic bending, and statistical analysis shows that kinks are not localized within any single sequence element. A surprisingly small free energy is associated with kink formation.
一种带有磁振荡探针的新型原子力显微镜,提供了对自发吸附在云母上并在二价离子存在下原位成像的小DNA片段前所未有的分辨率。在由串联重复的d(A)5和d(GGGCC[C])序列组成的轴向应变小环中观察到扭结(平均角度为78度的局部弯曲)。与1 mM Mg2+相比,在1 mM Zn2+存在下,相同小环中扭结的频率增加了4倍。扭结在Mg2+/Zn2+混合电解质中持续存在,直到Zn2+浓度降至100 microM以下,这表明这种类型的扭结可能在生理条件下发生。扭结似乎取代了固有弯曲,统计分析表明扭结并不局限于任何单个序列元件内。扭结形成所涉及的自由能出奇地小。