Transcription regulation of the type II restriction-modification system AhdI.
Transcription regulation of the type II restriction-modification system AhdI.
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DOI：
10.1093/nar/gkm1116
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发表时间：
2008-03
影响因子：
14.9
通讯作者：
Severinov K
中科院分区：
文献类型：
--
作者：
Bogdanova E;Djordjevic M;Papapanagiotou I;Heyduk T;Kneale G;Severinov K
限制修饰系统AhdI包含两个会聚转录单位，一个具有编码甲基转移酶亚基M和S的基因，另一个具有编码控制子（C）蛋白和限制性内切酶（R）的基因。我们表明，AhdI转录是由两个独立的调控环，是很好的优化，以确保成功建立在一个幼稚的细菌宿主。通过与启动子的-10元件重叠的AhdI位点的甲基化减弱来自强MS启动子的转录。弱CR启动子的转录受C蛋白与两个DNA结合位点相互作用的调节。与启动子远端高亲和力位点的相互作用激活转录，而与较弱的启动子近端位点的相互作用抑制它。由于高水平的协同性，在RNA聚合酶的情况下，两个C蛋白结合位点总是被占据，这就提出了一个问题，即如何实现激活的转录。我们开发了一个数学模型，是在定量协议的实验，并表明RNA聚合酶竞争C蛋白从启动子近端结合位点。这种不寻常的机制导致R基因转录的非常低效的激活，这可能有助于控制细胞中核酸内切酶的水平。
The Restriction-modification system AhdI contains two convergent transcription units, one with genes encoding methyltransferase subunits M and S and another with genes encoding the controller (C) protein and the restriction endonuclease (R). We show that AhdI transcription is controlled by two independent regulatory loops that are well-optimized to ensure successful establishment in a naïve bacterial host. Transcription from the strong MS promoter is attenuated by methylation of an AhdI site overlapping the -10 element of the promoter. Transcription from the weak CR promoter is regulated by the C protein interaction with two DNA-binding sites. The interaction with the promoter-distal high-affinity site activates transcription, while interaction with the weaker promoter-proximal site represses it. Because of high levels of cooperativity, both C protein-binding sites are always occupied in the absence of RNA polymerase, raising a question how activated transcription is achieved. We develop a mathematical model that is in quantitative agreement with the experiment and indicates that RNA polymerase outcompetes C protein from the promoter-proximal-binding site. Such an unusual mechanism leads to a very inefficient activation of the R gene transcription, which presumably helps control the level of the endonuclease in the cell.