Department of General Microbiology, Institute of Microbiology and Genetics, Georg-August University Göttingen, Göttingen, Germany.
J Bacteriol. 2013 May;195(10):2146-54. doi: 10.1128/JB.00117-13. Epub 2013 Mar 8.
Bacillus subtilis transports β-glucosides such as salicin by a dedicated phosphotransferase system (PTS). The expression of the β-glucoside permease BglP is induced in the presence of the substrate salicin, and this induction requires the binding of the antiterminator protein LicT to a specific RNA target in the 5' region of the bglP mRNA to prevent the formation of a transcription terminator. LicT is composed of an N-terminal RNA-binding domain and two consecutive PTS regulation domains, PRD1 and PRD2. In the absence of salicin, LicT is phosphorylated on PRD1 by BglP and thereby inactivated. In the presence of the inducer, the phosphate group from PRD1 is transferred back to BglP and consequently to the incoming substrate, resulting in the activation of LicT. In this study, we have investigated the intracellular localization of LicT. While the protein was evenly distributed in the cell in the absence of the inducer, we observed a subpolar localization of LicT if salicin was present in the medium. Upon addition or removal of the inducer, LicT rapidly relocalized in the cells. This dynamic relocalization did not depend on the binding of LicT to its RNA target sites, since the localization pattern was not affected by deletion of all LicT binding sites. In contrast, experiments with mutants affected in the PTS components as well as mutations of the LicT phosphorylation sites revealed that phosphorylation of LicT by the PTS components plays a major role in the control of the subcellular localization of this RNA-binding transcription factor.
枯草芽孢杆菌通过特定的磷酸转移酶系统（PTS）运输β-葡萄糖苷，如柳醇。在底物柳醇存在的情况下，β-葡萄糖苷透性酶 BglP 的表达被诱导，这种诱导需要终止子蛋白 LicT 结合到 bglP mRNA 5'区域的特定 RNA 靶位，以防止转录终止子的形成。LicT 由一个 N 端 RNA 结合域和两个连续的 PTS 调节域 PRD1 和 PRD2 组成。在没有柳醇的情况下，LicT 在 PRD1 上被 BglP 磷酸化而失活。在诱导物存在的情况下，PRD1 上的磷酸基团被回收到 BglP 上，进而被输入的底物接收，从而激活 LicT。在这项研究中，我们研究了 LicT 的细胞内定位。在没有诱导物的情况下，蛋白质在细胞中均匀分布，但如果培养基中存在柳醇，我们观察到 LicT 的亚极定位。当添加或去除诱导物时，LicT 在细胞中迅速重新定位。这种动态的重新定位并不依赖于 LicT 与它的 RNA 靶位的结合，因为定位模式不受删除所有 LicT 结合位的影响。相比之下，在 PTS 成分突变体和 LicT 磷酸化位点突变体的实验中，发现 LicT 的磷酸化由 PTS 成分介导，在控制这种 RNA 结合转录因子的亚细胞定位中起着主要作用。
