Sharma Ashima K, Payne Shelley M
Section of Molecular Genetics and Microbiology, The University of Texas at Austin, Austin, TX 78712, USA.
Mol Microbiol. 2006 Oct;62(2):469-79. doi: 10.1111/j.1365-2958.2006.05376.x.
Hfq plays an important role in cellular physiology by regulating the expression of several genes. Hfq synthesis in Escherichia coli is subject to auto-repression at translational level. Studies with Shigella flexneri show that hfq transcription is regulated by a pleiotropic regulator, DksA. Comparison of gene expression profiles of wild type and dksA mutant S. flexneri determined that hfq expression was reduced in the dksA mutant. As DksA is required for stress resistance and plaque formation in cultured cell monolayers, a measure of virulence, we assessed the role of Hfq in the dksA virulence phenotype. Expression of hfq in the dksA mutant restored plaque formation, and an hfq mutant failed to form plaques. Thus, DksA plays a role in regulating hfq gene expression and this regulation is important for S. flexneri virulence. In an in vitro transcription assay, addition of DksA increased transcription of hfq and this effect was greatest with one of the known hfq promoters. Addition of ppGpp, a stringent response molecule, along with DksA in the in vitro transcription assay resulted in a further increase in transcription of hfq, indicating that DksA is required for maximal transcription of hfq during both exponential and stringent response growth conditions.
Hfq通过调控多个基因的表达在细胞生理学中发挥重要作用。大肠杆菌中Hfq的合成在翻译水平受到自我抑制。对福氏志贺菌的研究表明，hfq转录受多效调节因子DksA调控。通过比较野生型和dksA突变型福氏志贺菌的基因表达谱，确定dksA突变体中hfq表达降低。由于DksA是培养细胞单层中抗应激和噬菌斑形成（一种毒力指标）所必需的，我们评估了Hfq在dksA毒力表型中的作用。在dksA突变体中表达hfq可恢复噬菌斑形成，而hfq突变体则无法形成噬菌斑。因此，DksA在调控hfq基因表达中发挥作用，且这种调控对福氏志贺菌的毒力很重要。在体外转录试验中，添加DksA可增加hfq的转录，并且在已知的hfq启动子之一中这种效应最为显著。在体外转录试验中，将严格反应分子ppGpp与DksA一起添加会导致hfq转录进一步增加，这表明在指数生长和严格反应生长条件下，DksA是hfq最大转录所必需的。
