Aviv M, Giladi H, Schreiber G, Oppenheim A B, Glaser G
Department of Cellular Biochemistry, Hebrew University--Hadassah Medical School, Jerusalem, Israel.
Mol Microbiol. 1994 Dec;14(5):1021-31. doi: 10.1111/j.1365-2958.1994.tb01336.x.
Transcriptional control of the himA and the himD/hip genes coding for the two subunits of the integration host factor (IHF) was investigated. The promoters for the two genes were identified by the use of primer extension and S1 analysis. Expression from both promoters was found to increase as the cells enter stationary phase. Mutation in rpoS, known to be induced upon entry to stationary phase, dramatically reduced the growth-phase response of the himA P4 promoter but had only a small effect on the induction of the himD/hip promoter. The increased activity of both promoters required the presence of the relA and spoT genes, suggesting that ppGpp plays a major role in the response to stationary phase. An artificial increase in ppGpp in exponentially growing cells induced a rapid increase in himA P4 and himD/hip mRNA levels. Experiments with a mutant defective in rpoS showed that the response of the himA P4 promoter to high ppGpp levels was greatly reduced while that of himD/hip was only slightly affected. Therefore, it seems that different mechanisms involving RpoS and ppGpp regulate the growth-phase response of the two promoters. We propose that the effect of ppGpp on himA P4 is mediated via RpoS whereas the himD/hip promoter is affected by ppGpp independently of RpoS. Expression of the himD/hip and himA genes was found to be subject to negative autoregulation. IHF-binding sites, implicated in autoregulation, were found to overlap both the himD/hip and himA P4 promoters. An additional IHF-binding site was found upstream of the himD/hip promoter. All three sites show low binding affinity to IHF suggesting that autoregulation can take place only after sufficiently high levels of IHF accumulate in the cell.
对编码整合宿主因子（IHF）两个亚基的himA和himD/hip基因的转录调控进行了研究。通过引物延伸和S1分析确定了这两个基因的启动子。发现随着细胞进入稳定期，两个启动子的表达均增加。已知在进入稳定期时被诱导的rpoS突变，显著降低了himA P4启动子的生长阶段反应，但对himD/hip启动子的诱导仅产生较小影响。两个启动子活性的增加需要relA和spoT基因的存在，这表明ppGpp在对稳定期的反应中起主要作用。在指数生长期细胞中人为增加ppGpp会导致himA P4和himD/hip mRNA水平迅速增加。对rpoS缺陷突变体的实验表明，himA P4启动子对高ppGpp水平的反应大大降低，而himD/hip的反应仅受到轻微影响。因此，似乎涉及RpoS和ppGpp的不同机制调节了两个启动子的生长阶段反应。我们提出，ppGpp对himA P4的作用是通过RpoS介导的，而himD/hip启动子受ppGpp的影响独立于RpoS。发现himD/hip和himA基因的表达受到负向自动调节。与自动调节有关的IHF结合位点被发现与himD/hip和himA P4启动子均重叠。在himD/hip启动子上游发现了一个额外的IHF结合位点。所有三个位点对IHF的结合亲和力都很低，这表明只有在细胞中积累了足够高水平的IHF后才会发生自动调节。
