School of Biological Sciences, Chung-Ang University, Seoul, Republic of Korea.
J Bacteriol. 2012 May;194(9):2214-20. doi: 10.1128/JB.00099-12. Epub 2012 Feb 17.
In Escherichia coli, the corA gene encodes a transporter that mediates the influx of Co(2+), Mg(2+), and Ni(2+) into the cell. During the course of experiments aimed at identifying RNase III-dependent genes in E. coli, we observed that steady-state levels of corA mRNA as well as the degree of cobalt influx into the cell were dependent on cellular concentrations of RNase III. In addition, changes in corA expression levels by different cellular concentrations of RNase III were closely correlated with degrees of resistance of E. coli cells to Co(2+) and Ni(2+). In vitro and in vivo cleavage analyses of corA mRNA identified RNase III cleavage sites in the 5'-untranslated region of the corA mRNA. The introduction of nucleotide substitutions at the identified RNase III cleavage sites abolished RNase III cleavage activity on corA mRNA and resulted in prolonged half-lives of the mRNA, which demonstrates that RNase III cleavage constitutes a rate-determining step for corA mRNA degradation. These findings reveal an RNase III-mediated regulatory pathway that functions to modulate corA expression and, in turn, the influx of metal ions transported by CorA in E. coli.
在大肠杆菌中，corA 基因编码一种转运体，介导 Co(2+)、Mg(2+)和 Ni(2+)进入细胞。在旨在鉴定大肠杆菌中 RNase III 依赖性基因的实验过程中，我们观察到 corA mRNA 的稳态水平以及钴流入细胞的程度依赖于细胞中 RNase III 的浓度。此外，不同细胞浓度的 RNase III 对 corA 表达水平的改变与大肠杆菌细胞对 Co(2+)和 Ni(2+)的抗性程度密切相关。corA mRNA 的体外和体内切割分析鉴定了 corA mRNA 5'非翻译区的 RNase III 切割位点。在鉴定的 RNase III 切割位点引入核苷酸取代会使 corA mRNA 上的 RNase III 切割活性丧失，并导致 mRNA 的半衰期延长，这表明 RNase III 切割是 corA mRNA 降解的限速步骤。这些发现揭示了一种由 RNase III 介导的调节途径，该途径可调节 corA 的表达，进而调节由 CorA 在大肠杆菌中转运的金属离子的流入。
