Department of Microbiology and Cell Biology, Indian Institute of Science, Bangalore 560012, India.
Proc Natl Acad Sci U S A. 2012 May 15;109(20):E1287-93. doi: 10.1073/pnas.1119226109. Epub 2012 Apr 16.
Most bacterial genomes harbor restriction-modification systems, encoding a REase and its cognate MTase. On attack by a foreign DNA, the REase recognizes it as nonself and subjects it to restriction. Should REases be highly specific for targeting the invading foreign DNA? It is often considered to be the case. However, when bacteria harboring a promiscuous or high-fidelity variant of the REase were challenged with bacteriophages, fitness was maximal under conditions of catalytic promiscuity. We also delineate possible mechanisms by which the REase recognizes the chromosome as self at the noncanonical sites, thereby preventing lethal dsDNA breaks. This study provides a fundamental understanding of how bacteria exploit an existing defense system to gain fitness advantage during a host-parasite coevolutionary "arms race."
大多数细菌基因组都携带有限制修饰系统，编码 REase 和其同源的 MTase。当受到外来 DNA 的攻击时，REase 将其识别为非自身，并对其进行限制。REase 是否应该针对入侵的外源 DNA 具有高度特异性？通常认为情况就是如此。然而，当带有 REase 混杂或高保真变体的细菌受到噬菌体的挑战时，在催化混杂的条件下，适应性达到最大值。我们还描述了 REase 如何在非典型位点识别染色体为自身，从而防止致命的双链 DNA 断裂的可能机制。这项研究提供了对细菌如何利用现有防御系统在宿主-寄生虫共同进化的“军备竞赛”中获得适应性优势的基本理解。
