DNA supercoiling, a critical signal regulating the basal expression of the lac operon in Escherichia coli.
DNA supercoiling, a critical signal regulating the basal expression of the lac operon in Escherichia coli.
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DOI：
10.1038/srep19243
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发表时间：
2016-01-14
影响因子：
4.6
通讯作者：
Leng F
中科院分区：
文献类型：
--
作者：
Fulcrand G;Dages S;Zhi X;Chapagain P;Gerstman BS;Dunlap D;Leng F
大肠杆菌lac阻遏因子（LacI）是控制lac操纵子中lacZYA表达的典型转录因子。这种四聚体蛋白特异性地与lac操纵子的O1、O2和O3操作符结合，形成一个DNA环，抑制来自相邻lac启动子的转录。在这篇文章中，我们证明了在O1和O2操作符的天然位置上，LacI约束了lac启动子401-bp DNA环内的三个（−）超级线圈，并形成了拓扑屏障。laci介导的DNA拓扑屏障的稳定性与其DNA结合亲和力成正比。然而，我们发现DNA超卷曲调节了大肠杆菌中lac操纵子的基础表达。我们的结果与假设一致，即LacI作为一种拓扑屏障，在lac启动子的401-bp DNA环内约束自由、无约束（−）超级线圈。这些受限的（−）超级线圈增强了LacI的dna结合亲和力，从而抑制了启动子。因此，在不同的生长条件下，LacI结合被超螺旋调节以控制lacZYA在lac操纵子中的表达。
Escherichia coli lac repressor (LacI) is a paradigmatic transcriptional factor that controls the expression of lacZYA in the lac operon. This tetrameric protein specifically binds to the O1, O2 and O3 operators of the lac operon and forms a DNA loop to repress transcription from the adjacent lac promoter. In this article, we demonstrate that upon binding to the O1 and O2 operators at their native positions LacI constrains three (−) supercoils within the 401-bp DNA loop of the lac promoter and forms a topological barrier. The stability of LacI-mediated DNA topological barriers is directly proportional to its DNA binding affinity. However, we find that DNA supercoiling modulates the basal expression from the lac operon in E. coli. Our results are consistent with the hypothesis that LacI functions as a topological barrier to constrain free, unconstrained (−) supercoils within the 401-bp DNA loop of the lac promoter. These constrained (−) supercoils enhance LacI’s DNA-binding affinity and thereby the repression of the promoter. Thus, LacI binding is superhelically modulated to control the expression of lacZYA in the lac operon under varying growth conditions.