Multiple hok genes on the chromosome of Escherichia coli
Multiple hok genes on the chromosome of Escherichia coli
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DOI：
10.1046/j.1365-2958.1999.01431.x
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发表时间：
1999-06-01
影响因子：
3.6
通讯作者：
Gerdes, K
中科院分区：
文献类型：
--
作者：
Pedersen, K;Gerdes, K
R1HOK/SOK位点通过杀死无质粒细胞而介导了质粒的稳定。许多细菌质粒携带相似的基因座，例如，F质粒携带两个HOK同源物，flm和srnB，它们通过这种特殊类型的程序性细胞死亡来调节质粒的稳定。在这里，我们证明了大肠杆菌K-12的染色体编码了5个HOK同源基因座，所有这些基因座都指定了HOK样毒素。其中三个位点似乎被插入元件IS150或IS186失活，位于毒素编码读框(即HokA、HokC和Hoke)附近但不在其中，一个系统可能通过点突变(HokB)失活，而第五个系统可能通过重大基因重排(HokD)失活。在野生型大肠杆菌的EcoR库中，我们发现了不含IS元件的HokA和HokC基因座。分子和遗传分析表明，HokA和hokC基因座指定了不稳定的反义RNA和稳定的编码毒素的mRNAs，它们在其3‘端被加工。对mRNA序列的比对揭示了所有已知的调控元件，这些调控元件需要对质粒编码的mRNAs进行非常正确的折叠和再折叠。保守的元件包括确保全长mRNAs中长范围相互作用的FBI，以及TAO和反义RNA靶向翻译和处理后的mRNAs快速反义RNA结合所需的茎环。我们一致地发现，染色体编码的mRNAs在其3‘端被处理，导致推测的翻译活性mRNAs。尽管存在所有的调控元件，但染色体编码的基因座并不存在：通过杀死无质粒细胞来调节质粒的稳定。染色体编码的mRNAs在体外翻译得很差，从而解释了缺乏表型的原因。这些观察结果表明，染色体上的HOK样基因可能是由一种未知的信号诱导的。
The hok/sok locus of plasmid R1 mediates plasmid stabilization by the killing of plasmid-free cells. Many bacterial plasmids carry similar loci, For example, the F plasmid carries two hok homologues, flm and srnB, that mediate plasmid stabilization by this specialized type of programmed cell death. Here, we show that the chromosome of E. coli K-12 codes for five hok homologous loci, all of which specify Hok-like toxins. Three of the loci appear to be inactivated by the insertion elements IS 150 or IS186 located close to but not in the toxin-encoding reading frames (i.e. hokA, hokC and hokE), one system is probably inactivated by point mutation (hokB), whereas the fifth system is inactivated by a major genetic rearrangement (hokD). In the ECOR collection of wild-type E. coli strains, we identified hokA and hokC loci without IS elements. A molecular and a genetic analysis show that the hokA and hokC loci specify unstable antisense RNAs and stable toxin-encoding mRNAs that are processed at their 3' ends. An alignment of the mRNA sequences reveals all the regulatory elements known to be required far correct folding and refolding of the plasmid-encoded mRNAs. The conserved elements include fbi that ensure a long-range interaction in the full-length mRNAs, and tao and antisense RNA target stem-loops that are required for translation and rapid antisense RNA binding of the processed mRNAs. Consistently, we find that the chromosome-encoded mRNAs are processed at their 3' ends, resulting in the presumed translationally active mRNAs. Despite the presence of all of the regulatory elements, the chromosome-encoded loci do not: mediate plasmid stabilization by killing of plasmid-free cells. The chromosome-encoded mRNAs are poorly translated in vitro, thus yielding an explanation for the lacking phenotype. These observations suggest that the chromosomal hok-like genes may be induced by an as yet unknown signal.