Kang Dong-Min, Michon Christophe, Morinaga Tetsuro, Tanaka Kosei, Takenaka Shinji, Ishikawa Shu, Yoshida Ken-Ichi
Department of Agrobioscience, Graduate School of Agricultural Science, Kobe University, 1-1 Rokkodai, Nada, Kobe, 657-8501, Japan.
Present address: Department of Plant Medicine and RILS, Gyeongsang National University, Jinju, 52828, Republic of Korea.
BMC Microbiol. 2017 Jul 11;17(1):154. doi: 10.1186/s12866-017-1065-8.
Bacillus subtilis is able to utilize at least three inositol stereoisomers as carbon sources, myo-, scyllo-, and D-chiro-inositol (MI, SI, and DCI, respectively). NAD-dependent SI dehydrogenase responsible for SI catabolism is encoded by iolX. Even in the absence of functional iolX, the presence of SI or MI in the growth medium was found to induce the transcription of iolX through an unknown mechanism.
Immediately upstream of iolX, there is an operon that encodes two genes, yisR and iolQ (formerly known as degA), each of which could encode a transcriptional regulator. Here we performed an inactivation analysis of yisR and iolQ and found that iolQ encodes a repressor of the iolX transcription. The coding sequence of iolQ was expressed in Escherichia coli and the gene product was purified as a His-tagged fusion protein, which bound to two sites within the iolX promoter region in vitro.
IolQ is a transcriptional repressor of iolX. Genetic evidences allowed us to speculate that SI and MI might possibly be the intracellular inducers, however they failed to antagonize DNA binding of IolQ in in vitro experiments.
枯草芽孢杆菌能够利用至少三种肌醇立体异构体作为碳源，即肌醇（myo-）、 scyllo-肌醇和D-手性肌醇（分别为MI、SI和DCI）。负责SI分解代谢的NAD依赖性SI脱氢酶由iolX编码。即使在缺乏功能性iolX的情况下，也发现生长培养基中SI或MI的存在会通过未知机制诱导iolX的转录。
在iolX的紧邻上游，有一个操纵子编码两个基因，yisR和iolQ（以前称为degA），每个基因都可以编码一个转录调节因子。在这里，我们对yisR和iolQ进行了失活分析，发现iolQ编码iolX转录的阻遏物。iolQ的编码序列在大肠杆菌中表达，基因产物被纯化为His标签融合蛋白，该蛋白在体外与iolX启动子区域内的两个位点结合。
IolQ是iolX的转录阻遏物。遗传学证据使我们推测SI和MI可能是细胞内诱导物，然而在体外实验中它们未能拮抗IolQ与DNA的结合。
