Silencing of DNase Colicin E8 Gene Expression by a Complex Nucleoprotein Assembly Ensures Timely Colicin Induction.
Silencing of DNase Colicin E8 Gene Expression by a Complex Nucleoprotein Assembly Ensures Timely Colicin Induction.
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DOI：
10.1371/journal.pgen.1005354
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发表时间：
2015-06
期刊：
影响因子：
4.5
通讯作者：
Butala M
中科院分区：
文献类型：
--
作者：
Kamenšek S;Browning DF;Podlesek Z;Busby SJ;Žgur-Bertok D;Butala M
大肠杆菌素是质粒编码的窄谱抗生素，由大肠杆菌菌株合成并控制种内竞争。在先前的报告中，我们证明了全局转录因子IscR与DNA损伤反应的主调节因子莱克萨（LexA）共依赖性地延迟SOS诱导后孔形成大肠杆菌素基因的诱导。在这里，我们表明，IscR是不参与调节核酸酶大肠杆菌素，但AsnC蛋白。我们报告说，AsnC，在音乐会与莱克萨，是关键的控制器的时间诱导的DNA降解大肠杆菌素E8基因（cea 8），DNA损伤后。我们表明，一个大的AsnC核小体样结构，在与两个莱克萨分子，阻止cea 8转录起始和AsnC结合活性直接调制L天冬酰胺。我们发现，L-天冬酰胺是一个环境因素，有显着的影响cea 8启动子调控。我们的研究结果表明，AsnC也调节其他几个DNase和RNase大肠杆菌素基因的表达，但并没有实质性影响成孔大肠杆菌素K基因的表达。我们认为，选择压力已经“选择”了高度保守的调控因子来控制大肠杆菌素的表达。大肠杆菌菌株，使类似的大肠杆菌素基因沉默的细菌之间交换大肠杆菌素质粒。大肠杆菌素被认为是研究细菌毒素的模型蛋白。这些窄谱抗生素可以通过多种机制杀死，例如通过在易感细胞的膜中形成孔或通过降解其核酸。大肠杆菌素基因由质粒编码，并被DNA损伤反应的主要调节因子莱克萨抑制。几个成孔大肠杆菌素基因的诱导也被IscR抑制，这确保了大肠杆菌素基因在DNA损伤细胞中，当营养耗尽时作为最后手段被打开。在这里，我们表明，核酸酶大肠杆菌素基因不受IscR的控制，但AsnC蛋白，在音乐会与莱克萨，是直接负责解偶联的直接表达的DNA酶大肠杆菌素E8的SOS反应的主要诱导。AsnC将大肠杆菌素E8启动子的DNA包裹成复杂的核蛋白组装体，并且该复合体的结构因氨基酸L-天冬酰胺的存在而改变。因此，代谢物响应性和DNA损伤响应性调节剂的抑制作用在不同大肠杆菌素的调节区域起作用。因此，对几种环境信号的反应已经被整合，以确保在DNA损伤后，大肠杆菌素的合成仅在终末损伤的细胞中被紧密抑制和诱导。
Colicins are plasmid-encoded narrow spectrum antibiotics that are synthesized by strains of Escherichia coli and govern intraspecies competition. In a previous report, we demonstrated that the global transcriptional factor IscR, co dependently with the master regulator of the DNA damage response, LexA, delays induction of the pore forming colicin genes after SOS induction. Here we show that IscR is not involved in the regulation of nuclease colicins, but that the AsnC protein is. We report that AsnC, in concert with LexA, is the key controller of the temporal induction of the DNA degrading colicin E8 gene (cea8), after DNA damage. We demonstrate that a large AsnC nucleosome-like structure, in conjunction with two LexA molecules, prevent cea8 transcription initiation and that AsnC binding activity is directly modulated by L asparagine. We show that L-asparagine is an environmental factor that has a marked impact on cea8 promoter regulation. Our results show that AsnC also modulates the expression of several other DNase and RNase colicin genes but does not substantially affect pore-forming colicin K gene expression. We propose that selection pressure has “chosen” highly conserved regulators to control colicin expression in E. coli strains, enabling similar colicin gene silencing among bacteria upon exchange of colicinogenic plasmids. Colicins are considered model proteins for studying bacterial toxins. These narrow spectrum antibiotics can kill by a variety of mechanisms, e.g. by forming pores in the membranes of susceptible cells or by degrading their nucleic acids. Colicin genes are plasmid-encoded and repressed by the master regulator of the DNA damage response, LexA. Induction of several pore-forming colicin genes is also repressed by IscR, which ensures that colicin genes are switched on as a last resort in DNA damaged cells, when nutrients are depleted. Here we show that nuclease colicin genes are not controlled by IscR but that the AsnC protein, in concert with LexA, is directly responsible for uncoupling the immediate expression of the DNase colicin E8 from the main induction of the SOS response. AsnC wraps the DNA of the colicin E8 promoter into a complex nucleoprotein assembly and the architecture of this complex is altered by the presence of the amino acid L-asparagine. Thus, repression by metabolite-responsive and DNA-damage responsive regulators operates at the regulatory regions of different colicins. Hence, the response to several environmental signals have been integrated to ensure that, following DNA damage, colicin synthesis is tightly repressed and induced only in terminally damaged cells.
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