Structural analysis of the genetic switch controlling expression of the AhdI restriction-modification system

所有生物体中基因表达的调控都依赖于基因调控蛋白与其DNA靶标之间复杂的相互作用。要充分了解这种机制，需要在生物物理和生物化学层面进行分析。在这里，我们调查的基因开关参与细菌限制修饰系统的调节的分子基础。细菌中的限制修饰系统作为原始“免疫系统”的一种形式;它们识别外来DNA序列并能够破坏入侵的DNA。然而，破坏DNA的酶的基因的表达必须被延迟，以便宿主DNA有时间被标记为“自身”（通过一个称为甲基化的过程），从而防止切割。一个控制蛋白负责这种时间延迟，我们已经解决了它的分子结构的X射线衍射。我们还确定了蛋白质与其靶DNA序列相互作用时形成许多复合物。该项目的目的是发现与DNA结合的各种调控复合物的三维结构，并了解它们如何相互作用以调控相关基因。总之，这些实验方法应该提供一个详细的分子图片的限制修饰系统的建立和维护的基础上的遗传开关，其中许多功能应该是普遍适用于广泛的基因调控系统。

The regulation of gene expression in all organisms is dependent on complex interactions between gene-regulatory proteins and their DNA targets. A full understanding of such mechanisms requires analysis at the biophysical and biochemical level. Here, we investigate the molecular basis of the genetic switch involved in the regulation of bacterial restriction-modification systems. Restriction-modification systems in bacteria act as a form of primitive 'immune system'; they recognise foreign DNA sequences and are able to destroy invading DNA. However, expression of the gene for the enzyme that destroys the DNA must be delayed, to allow time for the host DNA to become labelled as 'self' (by a process called methylation) and thus protected from cleavage. A controller protein is responsible for this timing delay, and we have solved its molecular structure by X-ray diffraction. We have also established that the protein forms a number of complexes when it interacts with its target DNA sequence. The aim of this project is to discover the 3-dimensional structure of the various regulatory complexes bound to DNA, and to understand how they interact to allow regulation of the relevant genes. Together, these experimental approaches should provide a detailed molecular picture of the genetic switch underlying the establishment and maintenance of restriction-modification systems, many features of which should be generally applicable to a wide range of gene regulatory systems.