Afflerbach H, Schröder O, Wagner R
Institut für Physikalische Biologie, Heinrich-Heine-Universität Düsseldorf, Germany.
Mol Microbiol. 1998 May;28(3):641-53. doi: 10.1046/j.1365-2958.1998.00829.x.
The Escherichia coli DNA-binding protein H-NS is known to interact specifically with the upstream region of ribosomal RNA transcription units, where it causes transcriptional repression in vitro. Here, we present results demonstrating the effect of H-NS on rRNA transcription in vivo. rRNA synthesis rates were compared in cells that differ in the expression of functional H-NS or FIS molecules. We could show that in the absence of H-NS derepression of rRNA synthesis occurs at low growth rates. During the cell cycle H-NS is responsible for the rapid shut-off of rRNA synthesis at the end of the exponential phase. As it is known for FIS-dependent activation, the inhibitory function of H-NS is specific for P1, the first of the tandem rRNA promoters. The effect of H-NS on rRNA synthesis was further assessed under stress conditions. While under osmotic upshift the reduction in rRNA synthesis is clearly H-NS-dependent, no such influence could be detected at cold shock. Determination of the cellular ppGpp concentrations revealed that H-NS does not mediate its function via alterations in the synthesis of the global effector ppGpp.
已知大肠杆菌DNA结合蛋白H-NS可与核糖体RNA转录单元的上游区域特异性相互作用，在体外它会导致转录抑制。在此，我们展示了H-NS在体内对rRNA转录的影响。我们比较了功能性H-NS或FIS分子表达不同的细胞中的rRNA合成速率。我们发现，在缺乏H-NS的情况下，rRNA合成在低生长速率时会发生去抑制。在细胞周期中，H-NS负责在指数期末期快速关闭rRNA合成。正如FIS依赖性激活一样，H-NS的抑制功能对串联rRNA启动子中的第一个启动子P1具有特异性。我们还在应激条件下进一步评估了H-NS对rRNA合成的影响。虽然在渗透压升高时rRNA合成的减少明显依赖于H-NS，但在冷休克时未检测到这种影响。细胞内ppGpp浓度的测定表明，H-NS并非通过改变全局效应分子ppGpp的合成来介导其功能。
