DNA supercoiling changes the spacing requirement of two lac operators for DNA loop formation with lac repressor.
DNA supercoiling changes the spacing requirement of two lac operators for DNA loop formation with lac repressor.
复制标题
DNA 超螺旋改变了使用 lac 阻遏物形成 DNA 环时两个 lac 操纵子的间距要求。
作者：
Helmut Kramer;M. Amouyal;Alfred;Nordheim;B. Muller
我们用凝胶滞留实验研究了DNA超卷曲对Lac阻遏子和两个Lac操纵子之间的环形成的影响。构建了一系列大小相同的15个DNA小环(452bp)，携带两个Lac操作符，距离从153到168bp不等。低正或负超卷曲(Sigma=+/-0.023)改变了形成最稳定环所需的两个Lac操作符之间的间距。这揭示了在超螺旋DNA微环中存在改变的双螺旋重复序列(范围从10.3到10.7bp)。在升高的负超线圈(Sigma=−0.046)下，在测试的所有操作员距离上都形成了极其稳定的环路，并保留了轻微的间隔周期。在对含有拓扑异构酶I的小环-阻遏子复合体进行松弛后，发现在那些携带算子的小环中限制了一个超螺旋转角，距离对应于非整数个螺旋转角。这表明DNA环的形成可以定义具有改变的DNA螺旋拓扑性质的局部DNA结构域。
We have used a gel retardation assay to investigate the influence of DNA supercoiling on loop formation between lac repressor and two lac operators. A series of 15 DNA minicircles of identical size (452 bp) was constructed carrying two lac operators at distances ranging from 153 to 168 bp. Low positive or negative supercoiling (sigma = +/‐ 0.023) changed the spacing between the two lac operators required for the formation of the most stable loops. This reveals the presence of altered double helical repeats (ranging from 10.3 to 10.7 bp) in supercoiled DNA minicircles. At elevated negative supercoiling (sigma = −0.046) extremely stable loops were formed at all operator distances tested, with a slight spacing periodicity remaining. After relaxation of minicircle‐repressor complexes with topoisomerase I one superhelical turn was found to be constrained in those minicircles which carry operators at distances corresponding to a non‐integral number of helical turns. This indicates that DNA loop formation can define local DNA domains with altered topological properties of the DNA helix.