Department of Natural Resource Sciences, Faculty of Agricultural and Environmental Sciences, McGill University, Ste-Anne-de-Bellevue, QC, Canada.
Department of Microbiology and Immunology, Columbia University Medical Center, New York, NY, USA.
Microbiology (Reading). 2013 Aug;159(Pt 8):1649-1660. doi: 10.1099/mic.0.067983-0. Epub 2013 May 31.
Hfq is a small RNA-binding protein involved in the post-transcriptional regulation of gene expression by affecting the stability of the mRNA and by mediating efficient pairing between small regulatory RNAs and their target mRNAs. In Legionella pneumophila, the aetiological agent of Legionnaires' disease, mutation of hfq results in increased duration of the lag phase and reduced growth in low-iron medium. In an effort to uncover genes potentially regulated by Hfq, the transcriptome of an hfq mutant strain was compared to that of the wild-type. Unexpectedly, many genes located within a 100 kb genomic island, including a section of the previously identified efflux island, were overexpressed in the hfq mutant strain. Since this island contains a putative conjugative system and an integrase, it was postulated that it could be a new integrated mobile genetic element. PCR analysis revealed that this region exists both as an integrated and as an episomal form in the cell population and that it undergoes differential excision in the hfq mutant background, which was further confirmed by trans-complementation of the hfq mutation. This new plasmid-like element was named pLP100. Differential excision did not affect the copy number of pLP100 at the population level. This region contains a copper efflux pump encoded by copA, and increased resistance to copper was observed for the hfq mutant strain that was abrogated in the complemented strain. A strain carrying a mutation of hfq and a deletion of the right side recombination site, attR, showed that overexpression of pLP100 genes and increased copper resistance in the hfq mutant strain were dependent upon excision of pLP100.
Hfq 是一种小 RNA 结合蛋白，通过影响 mRNA 的稳定性以及介导小调控 RNA 与其靶 mRNA 之间的有效配对，参与基因表达的转录后调控。在嗜肺军团菌中，Hfq 的突变导致潜伏期延长和在低铁培养基中生长减少，嗜肺军团菌是军团病的病原体。为了揭示可能受 Hfq 调控的基因，我们比较了 hfq 突变株和野生型的转录组。出人意料的是，许多位于 100kb 基因组岛上的基因（包括先前鉴定的外排岛的一部分）在 hfq 突变株中过表达。由于该岛包含一个假定的易位系统和一个整合酶，因此推测它可能是一个新的整合移动遗传元件。PCR 分析显示，该区域在细胞群体中既以整合形式存在，也以附加体形式存在，并且在 hfq 突变背景下发生差异切除，这在 hfq 突变的互补实验中得到进一步证实。这个新的质粒样元件被命名为 pLP100。差异切除在群体水平上不影响 pLP100 的拷贝数。该区域包含由 copA 编码的铜外排泵，并且 hfq 突变株对铜的抗性增加，而在互补菌株中这种抗性被消除。携带 hfq 突变和右侧重组位点 attR 缺失的菌株表明，pLP100 基因的过表达和 hfq 突变株对铜的抗性增加依赖于 pLP100 的切除。
