Lazarus L R, Travers A A
MRC Laboratory of Molecular Biology, Cambridge, UK.
EMBO J. 1993 Jun;12(6):2483-94. doi: 10.1002/j.1460-2075.1993.tb05903.x.
The Escherichia coli DNA bending protein factor for inversion stimulation (FIS), is neither necessary nor responsible for the stimulation of transcription from the wild type promoter for the tyrT operon (encoding a species of tyrosine tRNA) that occurs upon resumption of exponential growth. This conclusion is unexpected given that the regulatory element required for optimal transcription of tyrT contains three binding sites for FIS protein. In addition, it is in apparent conflict with reports from other laboratories which have described FIS-dependent activation of the stable RNA promoters rrnB P1 and thrU(tufB) in vivo. However, tyrT transcription is stimulated in a FIS-dependent manner both in vivo and in vitro when promoter function is impaired by mutation of the promoter itself or by the addition of the polymerase effector guanosine 5'-diphosphate 3'-diphosphate. These conditions, which expose a requirement for activation of stable RNA synthesis by FIS, suggest that FIS serves an adaptive role permitting high levels of stable RNA transcription on nutritional shift-up when RNA polymerase levels are depleted. In principle such a mechanism could confer a significant selective advantage thus accounting for the conservation of FIS binding sites in the regulatory regions of stable RNA promoters.
大肠杆菌中用于刺激倒位的DNA弯曲蛋白因子（FIS），对于指数生长恢复时从野生型tyrT操纵子启动子（编码一种酪氨酸tRNA）刺激转录既不是必需的，也不负责这种刺激。鉴于tyrT最佳转录所需的调控元件包含三个FIS蛋白结合位点，这个结论出乎意料。此外，它与其他实验室的报告明显矛盾，那些报告描述了体内稳定RNA启动子rrnB P1和thrU（tufB）的FIS依赖性激活。然而，当启动子功能因启动子自身突变或添加聚合酶效应物鸟苷5'-二磷酸3'-二磷酸而受损时，tyrT转录在体内和体外均以FIS依赖性方式受到刺激。这些条件揭示了FIS对稳定RNA合成激活的需求，表明FIS起到一种适应性作用，当RNA聚合酶水平耗尽时，在营养物质上调时允许高水平的稳定RNA转录。原则上，这样一种机制可以赋予显著的选择优势，从而解释了稳定RNA启动子调控区域中FIS结合位点的保守性。
