Integrative and conjugative elements (ICEs) are chromosomally-integrated mobile genetic elements that excise from their host chromosome and transfer to other bacteria via conjugation. ICEMlSymR7A is the prototypical member of a large family of "symbiosis ICEs" which confer upon their hosts the ability to form a nitrogen-fixing symbiosis with a variety of legume species. Mesorhizobial symbiosis ICEs carry a common core of mobilisation genes required for integration, excision and conjugative transfer. IntS of ICEMlSymR7A enables recombination between the ICEMlSymR7A attachment site attP and the 3' end of the phe-tRNA gene. Here we identified putative IntS attP arm (P) sites within the attP region and demonstrated that the outermost P1 and P5 sites demarcated the minimal region for efficient IntS-mediated integration. We also identified the ICEMlSymR7A origin-of-transfer (oriT) site directly upstream of the relaxase-gene rlxS. The ICEMlSymR7A conjugation system mobilised a plasmid carrying the cloned oriT to Escherichia coli in an rlxS-dependent manner. Surprisingly, an in-frame, markerless deletion mutation in the ICEMlSymR7A recombination directionality factor (excisionase) gene rdfS, but not a mutation in intS, abolished mobilisation, suggesting the rdfS deletion tentatively has downstream effects on conjugation or its regulation. In summary, this work defines two critical cis-acting regions required for excision and transfer of ICEMlSymR7A and related ICEs.

中文翻译：

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共生岛ICEMlSymR7A的整合附着和转移起点区域的描述。

整合和结合元件（ICE）是染色体整合的移动遗传元件，可从其宿主染色体上切除并通过结合转移至其他细菌。ICEMlSymR7A是“共生ICE”大家族的原型成员，这些ICE赋予它们的宿主与多种豆科植物物种形成固氮共生的能力。中生细菌共生ICEs具有整合，切除和接合转移所需的动员基因的共同核心。ICEM1SymR7A的IntS使ICEM1SymR7A附着位点attP与phe-tRNA基因的3'端重组。在这里，我们确定了attP区域内的推定IntS attP臂（P）位点，并证明了最外面的P1和P5位点划定了有效IntS介导的整合的最小区域。我们还确定了直接在松弛酶基因rlxS上游的ICEMlSymR7A转移起点（oriT）位点。ICEMlSymR7A偶联系统以rlxS依赖性方式将携带克隆的oriT的质粒动员到大肠杆菌中。出人意料的是，ICEMlSymR7A重组方向性因子（切除酶）基因rdfS中的框内无标记缺失突变，而不是intS中的突变，消除了动员，这表明rdfS缺失暂定对共轭或其调节具有下游作用。总之，这项工作定义了ICEMlSymR7A和相关ICE的切除和转移所需的两个关键的顺式作用区域。ICEMlSymR7A偶联系统以rlxS依赖性方式将携带克隆的oriT的质粒动员到大肠杆菌中。出人意料的是，ICEMlSymR7A重组方向性因子（切除酶）基因rdfS中的框内无标记缺失突变，而不是intS中的突变，消除了动员，这表明rdfS缺失暂定对共轭或其调节具有下游作用。总之，这项工作定义了ICEMlSymR7A和相关ICE的切除和转移所需的两个关键的顺式作用区域。ICEMlSymR7A偶联系统以rlxS依赖性方式将携带克隆的oriT的质粒动员到大肠杆菌中。出人意料的是，ICEMlSymR7A重组方向性因子（切除酶）基因rdfS中的框内无标记缺失突变，而不是intS中的突变，消除了动员，这表明rdfS缺失暂定对共轭或其调节具有下游作用。总之，这项工作定义了ICEMlSymR7A和相关ICE的切除和转移所需的两个关键的顺式作用区域。