Ueguchi C, Mizuno T
Laboratory of Microbiology, School of Agriculture, Nagoya University, Japan.
EMBO J. 1993 Mar;12(3):1039-46. doi: 10.1002/j.1460-2075.1993.tb05745.x.
The H-NS protein is a major constituent of the Escherichia coli nucleoid structure and is implicated in the compact organization of the chromosome. Based on recent genetic evidence, this protein appears to influence the transcription of a variety of apparently unlinked genes on the chromosome, although the underlying molecular mechanism is not fully understood. In this study, we carried out a series of in vitro transcription assays including purified H-NS with special reference to the osmotically inducible proV promoter of the proVWX operon (or proU), whose expression is known to be derepressed by lesions of the hns (osmZ) gene. Here, H-NS was revealed to selectively inhibit an early step(s) of proV transcription initiation through its direct binding to the promoter region. It was thus demonstrated that H-NS functions directly as a transcriptional repressor. Under the in vitro conditions used, this in vitro inhibitory effect of H-NS was affected by changes in the superhelical density of template DNAs and more significantly by the concentration of potassium (K+) ions. These results are also discussed with regard to the mechanism underlying regulation of the proV promoter in response to the medium osmolarity.
H-NS蛋白是大肠杆菌类核结构的主要成分，与染色体的紧密组织有关。基于最近的遗传学证据，尽管其潜在的分子机制尚未完全了解，但该蛋白似乎会影响染色体上各种明显不相关基因的转录。在本研究中，我们进行了一系列体外转录试验，包括使用纯化的H-NS，特别参考了proVWX操纵子（或proU）的渗透压诱导型proV启动子，已知其表达会因hns（osmZ）基因的损伤而解除抑制。在此，发现H-NS通过直接结合启动子区域选择性抑制proV转录起始的早期步骤。因此证明H-NS直接作为转录阻遏物发挥作用。在所使用的体外条件下，H-NS的这种体外抑制作用受模板DNA超螺旋密度变化的影响，更受钾（K+）离子浓度的显著影响。还就proV启动子响应培养基渗透压的调控机制对这些结果进行了讨论。
