DNA-Damaging Agents Induce the RecA-Independent Homologous Recombination Functions of Integrating Conjugative Elements of the SXT/R391 Family
DNA-Damaging Agents Induce the RecA-Independent Homologous Recombination Functions of Integrating Conjugative Elements of the SXT/R391 Family
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DOI：
10.1128/jb.02090-12
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发表时间：
2013-05-01
影响因子：
3.2
通讯作者：
Burrus, Vincent
中科院分区：
文献类型：
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作者：
Garriss, Genevieve;Poulin-Laprade, Dominic;Burrus, Vincent
SXT/R391 家族的整合接合元件 (ICE) 是抗生素抗性基因传播的主要贡献者。这些元件还通过其编码的不依赖于 RecA 的同源重组系统的作用促进 ICE 间重组，从而催化其自身的多样性。在这里，我们报道了这种由单链 DNA 退火蛋白 Bet 和核酸外切酶 Exo 组成的重组系统的表达是由 DNA 损伤剂通过 ICE 编码的转录调节因子诱导的。我们发现bet和exo基因是一个大的多顺反子转录本的一部分，其中包含许多保守的ICE基因，这些基因不参与主要的整合/切除和接合转移过程。我们表明，尽管重组基因高度转录，但它们的翻译受到额外的强大调节机制的影响。我们还表明，ICE 编码的推定单链 DNA 结合蛋白 (Ssb) 限制了杂合 ICE 的形成。最后，彻底的计算机分析表明，Bet 和 Exo 的直系同源物广泛分布在属于远缘相关细菌物种的细菌菌株中，并由各种移动遗传元件携带。系统发育分析表明，组成这些系统的退火蛋白和核酸外切酶有时具有不同的进化起源，强调了维持这些不相关的协作蛋白的功能的强大选择压力。
Integrating conjugative elements (ICEs) of the SXT/R391 family are major contributors to the spread of antibiotic resistance genes. These elements also catalyze their own diversity by promoting inter-ICE recombination through the action of the RecA-independent homologous recombination system that they encode. Here, we report that expression of this recombination system, which consists of the single-stranded DNA annealing protein Bet and the exonuclease Exo, is induced by DNA-damaging agents via ICE-encoded transcriptional regulators. We show that the bet and exo genes are part of a large polycistronic transcript that contains many conserved ICE genes that are not involved in the main integration/excision and conjugative transfer processes. We show that although the recombination genes are highly transcribed, their translation is subject to additional strong regulatory mechanisms. We also show that an ICE-encoded putative single-stranded DNA binding protein (Ssb) limits hybrid ICE formation. Finally, a thorough in silico analysis reveals that orthologues of Bet and Exo are widely distributed in bacterial strains belonging to very distantly related bacterial species and are carried by various mobile genetic elements. Phylogenetic analyses suggest that the annealing proteins and exonucleases that compose these systems sometimes have different evolutionary origins, underscoring the strong selective pressure to maintain the functionality of these unrelated cooperating proteins.