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首页> 外文期刊>Journal of bacteriology >The Transcriptional Factors MurR and Catabolite Activator Protein Regulate N-Acetylmuramic Acid Catabolism in Escherichia coli
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The Transcriptional Factors MurR and Catabolite Activator Protein Regulate N-Acetylmuramic Acid Catabolism in Escherichia coli

机译：转录因子MurR和分解代谢活化蛋白调节大肠杆菌中的N-乙酰基尿酸分解代谢。

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The MurNAc etherase MurQ of Escherichia coli is essential for the catabolism of the bacterial cell wall sugar N-acetylmuramic acid (MurNAc) obtained either from the environment or from the endogenous cell wall (i.e., recycling). High-level expression of murQ is required for growth on MurNAc as the sole source of carbon and energy, whereas constitutive low-level expression of murQ is sufficient for the recycling of peptidoglycan fragments continuously released from the cell wall during growth of the bacteria. Here we characterize for the first time the expression of murQ and its regulation by MurR, a member of the poorly characterized RpiR/AlsR family of transcriptional regulators. Deleting murR abolished the extensive lag phase observed for E. coli grown on MurNAc and enhanced murQ transcription some 20-fold. MurR forms a stable multimer (most likely a tetramer) and binds to two adjacent inverted repeats within an operator region. In this way MurR represses transcription from the murQ promoter and also interferes with its own transcription. MurNAc-6-phosphate, the substrate of MurQ, was identified as a specific inducer that weakens binding of MurR to the operator. Moreover, murQ transcription depends on the activation by cyclic AMP (cAMP)-catabolite activator protein (CAP) bound to a class I site upstream of the murQ promoter. murR and murQ are divergently orientated and expressed from nonoverlapping face-to-face (convergent) promoters, yielding transcripts that are complementary at their 5′ ends. As a consequence of this unusual promoter arrangement, cAMP-CAP also affects murR transcription, presumably by acting as a roadblock for RNA polymerase.
机译：大肠杆菌的MurNAc醚酶MurQ对于从环境或内源性细胞壁获得的细菌细胞壁糖 N -乙酰基尿酸（MurNAc）的分解代谢至关重要（即回收）。 murQ 的高水平表达是在MurNAc上生长（碳和能量的唯一来源）所必需的，而 murQ 的组成型低水平表达足以回收肽聚糖。细菌生长过程中，碎片不断从细胞壁释放出来。在这里，我们首次表征了 murQ 的表达及其由MurR的调控，MurR是特征性差的转录调控子RpiR / AlsR家族的成员。删除 murR 消除了 E观察到的广泛滞后阶段。大肠杆菌在MurNAc上生长，并增强 murQ 转录约20倍。 MurR形成稳定的多聚体（很可能是四聚体），并与操纵子区域内两个相邻的反向重复序列结合。这样，MurR抑制了 murQ 启动子的转录，并且还干扰了其自身的转录。 MurQ的底物MurNAc-6-磷酸被鉴定为一种特异性的诱导剂，可减弱MurR与操纵基因的结合。此外， murQ 转录取决于与 murQ 启动子上游I类位点结合的环AMP（cAMP）-分解代谢物激活蛋白（CAP）的激活。 murR 和 murQ 在非重叠的面对面（收敛）启动子上定向和表达，产生在5'末端互补的转录本。由于这种异常的启动子排列，cAMP-CAP也可能影响 murR 转录，可能是通过充当RNA聚合酶的障碍。

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