DNA distortion sequence recognition and the control of R-M gene expression

细菌使用所谓的限制性修饰（R-M）系统来保护自己免受外来DNA（例如细菌病毒）的入侵。R-M系统通过产生两种酶来工作。第一种是所谓的甲基转移酶(M)，它通过在战略位置添加甲基来标记细菌自身的DNA。第二种酶，一种核酸内切酶(R)，然后分解没有被正确标记的DNA。因此，R-M系统提供了一种选择性地破坏外源DNA的方法。然而，如果这两种酶的产生时间被打乱，核酸内切酶就会破坏细菌自身的DNA，导致细菌患上相当于自身免疫性疾病的疾病，并导致细菌死亡。为了避免这种情况，所谓的控制器(C)蛋白通过结合到控制单个R-M基因的DNA上的适当位点来调节这两种酶的合成。这导致了一个复杂的调节网络，有正的和负的“反馈”电路。我们的目标是准确理解DNA序列的细微变化是如何影响控制蛋白与基因控制区结合的强度，以及这是如何决定它们打开和关闭的顺序的。此外，我们想知道DNA的形状是如何扭曲的，以允许蛋白质与双螺旋结构相互作用，以及当蛋白质与DNA上相邻的位点结合时，这是如何参与协同作用的。一旦我们了解了这些分子细节，就有可能设计出针对不同细菌菌株的新型抗菌药物。

Bacteria use the so-called restriction-modification (R-M) system to protect themselves from invasion by foreign DNA (e.g. from bacterial viruses). The R-M system works by producing two enzymes. The first, a so-called methyltransferase (M), marks the bacterium's own DNA by adding methyl groups at strategic positions. The second enzyme, an endonuclease (R), then breaks down DNA that is not correctly marked. The R-M system thus provides a way to destroy foreign DNA selectively. However, if the timing of the production of the two enzymes is disturbed, the endonuclease will destroy the bacterium's own DNA, leading to the bacterial equivalent of an autoimmune disease and to death of the bacterium. To avoid this, so-called controller (C) proteins regulate the synthesis of the two enzymes by binding to the appropriate sites on the DNA that control the individual R-M genes. This leads to a complex regulatory network with positive and negative 'feedback' circuits. Our aim in this proposal is to understand exactly how subtle changes in the DNA sequence influence how strongly the controller protein binds to the control regions of the genes, and how this dictates the order in which they are switched on and off. Also, we want to know how the shape of the DNA is distorted to allow the proteins to interact with the double helix, and how this is involved in the synergy involved when proteins bind to adjacent sites on the DNA. Once we understand these things in molecular detail, it may be possible to design novel anti-bacterial drugs that are specific for different strains of bacteria.