Department of Biological Science and Technology, College of Biological Science and Technology, National Chiao Tung University, Hsinchu, Taiwan, Republic of China.
J Bacteriol. 2011 Oct;193(20):5833-40. doi: 10.1128/JB.05359-11. Epub 2011 Aug 12.
Glucose is a carbon source that is capable of modulating the level of cyclic AMP (cAMP)-regulated genes. In the present study, we found that the stability of ompA mRNA was reduced in Escherichia coli when glucose (40 mM) was present in Luria-Bertani (LB) medium. This effect was associated with a low level of cAMP induced by the glucose. The results were confirmed with an adenylyl cyclase mutant with low levels of cAMP that are not modulated by glucose. Northern blot and Western blot analyses revealed that the host factor I (Hfq) (both mRNA and protein) levels were downregulated in the presence of cAMP. Furthermore, we showed that a complex of cAMP receptor protein (CRP) and cAMP binds to a specific P3(hfq) promoter region of hfq and regulates hfq expression. The regulation of the hfq gene was confirmed in vivo using an hfq-deficient mutant transformed with an exogenous hfq gene containing the promoter. These results demonstrated that expression of hfq was repressed by the CRP-cAMP complex. The presence of glucose resulted in increased Hfq protein levels, which decreased ompA mRNA stability. An additional experiment showed that cAMP also increased the stability of fur mRNA. Taken together, these results suggested that the repression of Hfq by cAMP may contribute to the stability of other mRNA in E. coli.
葡萄糖是一种碳源，能够调节环腺苷酸 (cAMP) 调节基因的水平。在本研究中，我们发现当大肠杆菌在 LB 培养基中存在葡萄糖 (40mM) 时，ompA mRNA 的稳定性降低。这种效应与葡萄糖诱导的低水平 cAMP 有关。结果通过低水平 cAMP 的腺苷酸环化酶突变体得到证实，该突变体的 cAMP 不受葡萄糖调节。Northern blot 和 Western blot 分析表明，在 cAMP 存在的情况下，宿主因子 I (Hfq) (mRNA 和蛋白质) 水平下调。此外，我们表明，cAMP 受体蛋白 (CRP) 和 cAMP 的复合物与 hfq 的特定 P3(hfq) 启动子区域结合，并调节 hfq 的表达。通过含有启动子的外源 hfq 基因转化 hfq 缺陷突变体在体内证实了 hfq 基因的调控。这些结果表明 hfq 的表达受到 CRP-cAMP 复合物的抑制。葡萄糖的存在导致 Hfq 蛋白水平升高，ompA mRNA 稳定性降低。进一步的实验表明，cAMP 还增加了 fur mRNA 的稳定性。综上所述，这些结果表明 cAMP 对 Hfq 的抑制可能有助于大肠杆菌中其他 mRNA 的稳定性。
