Wang Xiao-Ling, Zhang Xing-Hua, Cao Meiwen, Zheng Hai-Zi, Xiao Bin, Wang Yilin, Li Ming
Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Key Laboratory of Colloid and Interface Science, Chinese Academy of Sciences, Beijing 100190, China.
J Phys Chem B. 2009 Feb 26;113(8):2328-32. doi: 10.1021/jp8078887.
Using a magnetic tweezers (MT) apparatus and an atomic force microscope (AFM), we studied the condensation of DNA induced by the cationic gemini surfactant hexyl-alpha,omega-bisdodecyldimethylammonium bromide (C12 C6 C12 Br2). Stepwise condensation events were found for forces from 0.5 to 4 pN, with a decrease in DNA extension by approximately 100 nm in each condensation event. Applied stretching forces larger than 6 pN were found to be able to decondense the condensates in a similar intermittent stepwise manner, but with approximately 60 nm of DNA released in each decondensation event. These observations are consistent with AFM images that show beadlike structures on DNA. The results lead to a model in which, during condensation, independent beadlike structures are initially formed on DNA, and as the local density of the beads increases, they compact into higher-order structures while maintaining their independence. The condensation process is different from any previously reported condensation process, but it is somewhat similar to that of chromatin assembly.
我们使用磁镊（MT）装置和原子力显微镜（AFM），研究了阳离子双子表面活性剂十六烷基-α,ω-双十二烷基二甲基溴化铵（C12 C6 C12 Br2）诱导的DNA凝聚。发现对于0.5至4 pN的力，存在逐步凝聚事件，每次凝聚事件中DNA伸展长度减少约100 nm。发现施加大于6 pN的拉伸力能够以类似的间歇性逐步方式使凝聚物解聚，但每次解聚事件中释放约60 nm的DNA。这些观察结果与显示DNA上珠状结构的AFM图像一致。结果得出一个模型，即在凝聚过程中，DNA上最初形成独立的珠状结构，随着珠子的局部密度增加，它们紧凑形成更高阶结构，同时保持其独立性。该凝聚过程不同于任何先前报道的凝聚过程，但在某种程度上类似于染色质组装过程。
