Expression of the chitobiose operon of Escherichia coli is regulated by three transcription factors:: NagC, ChbR and CAP
Expression of the chitobiose operon of Escherichia coli is regulated by three transcription factors:: NagC, ChbR and CAP
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DOI：
10.1111/j.1365-2958.2004.03986.x
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发表时间：
2004-04-01
影响因子：
3.6
通讯作者：
Pellegrini, O
中科院分区：
文献类型：
--
作者：
Plumbridge, J;Pellegrini, O
壳二糖操纵子chbBCARFG编码N-乙酰葡糖胺二糖壳二糖的转运和降解基因。壳二糖通过磷酸转移酶系统（PTS）转运，产生壳二糖-6P，壳二糖-6P被chbF基因产物水解为GlcNAc-6P，然后被nagBA基因产物进一步降解。chb操纵子的表达被NagC抑制，NagC调节参与氨基糖代谢的基因。NagC的诱导剂是GlcNAc-6P。NagC结合到由115 bp分开的两个位点，并且chb操纵子的转录起始点位于下游NagC操纵子内。此外，chb操纵子编码其自身的特异性调节因子ChbR，其为AraC型双重阻遏物-激活物，其结合到位于两个NagC位点之间的两个19 bp的直接重复序列。ChbR是在壳二糖存在下体内转录激活所必需的。操纵子的诱导也需要CAP，其结合到ChbR重复序列上游的位点。在不存在壳二糖的情况下，NagC和ChbR都充当阻遏物。这三个因素共同合作，将chb表达从抑制状态转换为激活状态。需要两种特异性诱导信号，一种用于ChbR以激活操纵子的表达，第二种用于NagC以解除其阻遏，确保只有当通过组合的chb-nag代谢途径有足够的通量以激活chb和nag操纵子两者的表达时，才诱导chb操纵子。
The chitobiose operon, chbBCARFG, encodes genes for the transport and degradation of the N-acetylglucosamine disaccharide, chitobiose. Chitobiose is transported by the phosphotransferase system (PTS) producing chitobiose-6P which is hydrolysed to GlcNAc-6P by the chbF gene product and then further degraded by the nagBA gene products. Expression of the chb operon is repressed by NagC, which regulates genes involved in amino sugar metabolism. The inducer for NagC is GlcNAc-6P. NagC binds to two sites separated by 115 bp and the transcription start point of the chb operon lies within the downstream NagC operator. In addition the chb operon encodes its own specific regulator, ChbR, an AraC-type dual repressor-activator, which binds to two direct repeats of 19 bp located between the two NagC sites. ChbR is necessary for transcription activation in the presence of chitobiose in vivo. Induction of the operon also requires CAP, which binds to a site upstream of the ChbR repeats. In the absence of chitobiose both NagC and ChbR act as repressors. Together these three factors cooperate in switching chb expression from the repressed to the activated state. The need for two specific inducing signals, one for ChbR to activate the expression of the operon and a second for NagC to relieve its repression, ensure that the chb operon is only induced when there is sufficient flux through the combined chb-nag metabolic pathway to activate expression of both the chb and nag operons.