Furrer P, Bednar J, Stasiak A Z, Katritch V, Michoud D, Stasiak A, Dubochet J
Laboratoire d'Analyse Ultrastructurale, Bâtiment de Biologie, Université de Lausanne, Switzerland.
J Mol Biol. 1997 Mar 7;266(4):711-21. doi: 10.1006/jmbi.1996.0825.
Using cryo-electron microscopy we reconstructed the three-dimensional trajectories adopted in cryovitrified solutions by double-stranded DNA molecules in which the backbone of one strand lacked a phosphate at regular intervals of 20 nucleotides. The shape of such nicked DNA molecules was compared with that of DNA molecules with exactly the same sequence but without any single-stranded scissions. Upon changing the salt concentration we observed opposite effects of charge neutralization on nicked and non-nicked DNA. In low salt solutions (10 mM Tris-HCl, 10 mM NaCl) the applied dense nicking caused ca 3.5-fold reduction of the DNA persistence length as compared with non-nicked DNA. Upon increasing the salt concentration (to 150 mM NaCl and 10 mM MgCl2) the persistence length of non-nicked DNA appreciably decreased while that of nicked DNA molecules increased by a factor of 2.
我们使用冷冻电子显微镜重建了双链DNA分子在冷冻玻璃化溶液中所采用的三维轨迹，其中一条链的主链每隔20个核苷酸就缺少一个磷酸基团。将这种有缺刻的DNA分子的形状与具有完全相同序列但没有任何单链切割的DNA分子的形状进行了比较。改变盐浓度时，我们观察到电荷中和对有缺刻和无缺刻DNA产生了相反的影响。在低盐溶液（10 mM Tris-HCl，10 mM NaCl）中，与无缺刻DNA相比，施加的密集缺刻导致DNA持久长度降低约3.5倍。随着盐浓度增加（至150 mM NaCl和10 mM MgCl2），无缺刻DNA的持久长度明显降低，而有缺刻DNA分子的持久长度增加了2倍。
