Laboratoire d'Ingénierie des Systèmes Macromoléculaires, CNRS-UPR 9027, Institut de Microbiologie de la Méditerranée, Aix-Marseille Université, Marseille, France.
PLoS Genet. 2011 Jul;7(7):e1002205. doi: 10.1371/journal.pgen.1002205. Epub 2011 Jul 28.
Type VI secretion systems (T6SS) are macromolecular machines of the cell envelope of Gram-negative bacteria responsible for bacterial killing and/or virulence towards different host cells. Here, we characterized the regulatory mechanism underlying expression of the enteroagregative Escherichia coli sci1 T6SS gene cluster. We identified Fur as the main regulator of the sci1 cluster. A detailed analysis of the promoter region showed the presence of three GATC motifs, which are target of the DNA adenine methylase Dam. Using a combination of reporter fusion, gel shift, and in vivo and in vitro Dam methylation assays, we dissected the regulatory role of Fur and Dam-dependent methylation. We showed that the sci1 gene cluster expression is under the control of an epigenetic switch depending on methylation: fur binding prevents methylation of a GATC motif, whereas methylation at this specific site decreases the affinity of Fur for its binding box. A model is proposed in which the sci1 promoter is regulated by iron availability, adenine methylation, and DNA replication.
VI 型分泌系统（T6SS）是革兰氏阴性菌细胞包膜的大型分子机器，负责细菌杀伤和/或对不同宿主细胞的毒力。在这里，我们描述了肠聚集性大肠杆菌 sci1 T6SS 基因簇表达的调控机制。我们确定 Fur 是 sci1 簇的主要调节剂。对启动子区域的详细分析表明存在三个 GATC 基序，这些基序是 DNA 腺嘌呤甲基酶 Dam 的靶标。通过报告融合、凝胶迁移、体内和体外 Dam 甲基化测定的组合，我们剖析了 Fur 和依赖 Dam 的甲基化的调节作用。我们表明，sci1 基因簇的表达受依赖于甲基化的表观遗传开关控制：fur 结合阻止 GATC 基序的甲基化，而该特定位点的甲基化降低 Fur 与其结合盒的亲和力。提出了一个模型，其中 sci1 启动子受铁可用性、腺嘌呤甲基化和 DNA 复制的调节。
