Interplay of transcriptional and small RNA-dependent control mechanisms regulates chitosugar uptake in Escherichia coli and Salmonella
Interplay of transcriptional and small RNA-dependent control mechanisms regulates chitosugar uptake in Escherichia coli and Salmonella
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DOI：
10.1111/mmi.12573
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发表时间：
2014-05-01
影响因子：
3.6
通讯作者：
Figueroa-Bossi, Nara
中科院分区：
文献类型：
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作者：
Plumbridge, Jacqueline;Bossi, Lionello;Figueroa-Bossi, Nara
大肠杆菌和沙门氏菌可以利用甲壳素衍生的寡糖作为碳源和氮源。壳糖通过专用的壳孔蛋白 ChiP 穿过外膜，并通过壳二糖转运蛋白 (ChbBCA) 跨细胞质膜转运。先前的工作表明，壳孔蛋白 ChiP 的合成需要 chbBCARFG 操纵子的转录。转录本 chbBC 部分的序列被证明可作为调节性小 RNA ChiX 的诱饵靶标，ChiX 通常会阻断 chiP 表达。 ChiX 在与 chbBC RNA 配对后不稳定并降解。在这里，我们发现 chiP 基因与 chbBCARFG 操纵子一样，也在转录水平上受到 NagC 阻遏物的下调。 NagC 抑制对于维持 chiP mRNA 水平相对于 ChiX 足够低至关重要，以允许该 sRNA 完全沉默。我们还表明，ChiX 与 chbBC RNA 配对在非诱导条件下（即当 ChiX 超过诱饵序列时）会下调 chbC。因此，在这些条件下，chbBC RNA 不仅仅是一个诱饵，而是 ChiX 调控的真正目标。总而言之，这些发现强调了化学计量在决定 sRNA 反应强度以及区分调节因子和调节目标方面的重要性。
Escherichia coli and Salmonella can use chitin-derived oligosaccharides as carbon and nitrogen sources. Chitosugars traverse the outer membrane through a dedicated chitoporin, ChiP, and are transported across the cytoplasmic membrane by the chitobiose transporter (ChbBCA). Previous work revealed that synthesis of the chitoporin, ChiP, requires transcription of the chbBCARFG operon. A sequence from the chbBC portion of the transcript was shown to act as a decoy target for a regulatory small RNA, ChiX, that normally blocks chiP expression. ChiX is destabilized and degraded upon pairing with chbBC RNA. Here, we show that the chiP gene, like the chbBCARFG operon, is also downregulated at the transcriptional level by the NagC repressor. NagC repression is critical in maintaining chiP mRNA levels low enough, relative to ChiX, to allow full silencing by this sRNA. We also show that pairing of ChiX to chbBC RNA downregulates chbC under uninduced conditions, that is, when ChiX is in excess to the decoy sequence. Hence, under these conditions, chbBC RNA is not just a decoy, but a true target of ChiX regulation. Altogether these findings underscore the importance of stoichiometry in dictating the strength of the sRNA response and in differentiating the regulator from the regulatory target.