Inácio José Manuel, Costa Carla, de Sá-Nogueira Isabel
Instituto de Tecnologia Química e Biológica, Universidade Nova de Lisboa, Avenida de República, Apartado 127, 2781-901 Oeiras, Portugal.
Faculdade de Ciências e Tecnologia, Universidade Nova de Lisboa, Quinta da Torre, 2829-516 Caparica, Portugal.
Microbiology (Reading). 2003 Sep;149(Pt 9):2345-2355. doi: 10.1099/mic.0.26326-0.
The Bacillus subtilis proteins involved in the utilization of L-arabinose are encoded by the araABDLMNPQ-abfA metabolic operon and by the araE/araR divergent unit. Transcription from the ara operon, araE transport gene and araR regulatory gene is induced by L-arabinose and negatively controlled by AraR. Additionally, expression of both the ara operon and the araE gene is regulated at the transcriptional level by glucose repression. Here, by transcriptional fusion analysis in different mutant backgrounds, it is shown that CcpA most probably complexed with HPr-Ser46-P plays the major role in carbon catabolite repression of the ara regulon by glucose and glycerol. Site-directed mutagenesis and deletion analysis indicate that two catabolite responsive elements (cres) present in the ara operon (cre araA and cre araB) and one cre in the araE gene (cre araE) are implicated in this mechanism. Furthermore, cre araA located between the promoter region of the ara operon and the araA gene, and cre araB placed 2 kb downstream within the araB gene are independently functional and both contribute to glucose repression. In Northern blot analysis, in the presence of glucose, a CcpA-dependent transcript consistent with a message stopping at cre araB was detected, suggesting that transcription 'roadblocking' of RNA polymerase elongation is the most likely mechanism operating in this system. Glucose exerts an additional repression of the ara regulon, which requires a functional araR.
枯草芽孢杆菌中参与L-阿拉伯糖利用的蛋白质由araABDLMNPQ-abfA代谢操纵子和araE/araR divergent单元编码。ara操纵子、araE转运基因和araR调控基因的转录由L-阿拉伯糖诱导，并受到AraR的负调控。此外，ara操纵子和araE基因的表达在转录水平上还受到葡萄糖阻遏的调节。在此，通过在不同突变背景下的转录融合分析表明，最有可能与HPr-Ser46-P复合的CcpA在葡萄糖和甘油对ara操纵子的碳分解代谢物阻遏中起主要作用。定点诱变和缺失分析表明，ara操纵子中存在的两个分解代谢物反应元件（cres）（cre araA和cre araB）以及araE基因中的一个cre（cre araE）与该机制有关。此外，位于ara操纵子启动子区域和araA基因之间的cre araA以及位于araB基因内下游2 kb处的cre araB具有独立功能，两者都对葡萄糖阻遏有贡献。在Northern印迹分析中，在葡萄糖存在的情况下，检测到一种与在cre araB处终止的信使一致的CcpA依赖性转录本，这表明RNA聚合酶延伸的转录“路障”是该系统中最可能起作用的机制。葡萄糖对ara操纵子施加额外的阻遏，这需要一个功能性的araR。
