Multiple mechanisms of transcription inhibition by ppGpp at the λρR promoter
Multiple mechanisms of transcription inhibition by ppGpp at the λρR promoter
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DOI：
10.1074/jbc.m208768200
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发表时间：
2002-11-15
影响因子：
4.8
通讯作者：
Hernandez, VJ
中科院分区：
文献类型：
--
作者：
Potrykus, K;Wegrzyn, G;Hernandez, VJ
细菌细胞中的一般应激条件引起称为严格应答的全局细胞应答。这种控制中的第一个事件是产生大量的调节核苷酸，鸟苷-3 '，5'-（双）焦磷酸（ppGpp）。最近提出ppGpp通过降低开放复合物在产生短寿命开放复合物的启动子（例如rRNA启动子）处的稳定性来起作用。然而，在这里，我们报告说，噬菌体pepdap（R）启动子，形成长寿命的开放复合物，抑制ppGpp在体外观察到在体内。我们对ppGpp对lambdap（R）处转录起始的特异性抑制进行了系统研究，发现ppGpp确实降低了lambdap（R）处开放复合物的稳定性，但只是轻微地降低。同样地，ppGpp对RNA聚合酶在dap（R）处的平衡结合常数和开放复合物形成速率也只有轻微的影响。ppGpp介导的抑制作用的主要作用是降低启动子逃逸的速率。我们的结论是，ppGpp介导的抑制转录起始不限于启动子，使短暂的开放复合物。相反，我们得出结论，转录物形成的初始催化步骤受到ppGpp的影响，特别是第一个磷酸二酯键的形成受到ppGpp at）dap（R）的抑制。
General stress conditions in bacterial cells cause a global cellular response called the stringent response. The first event in this control is production of large amounts of a regulatory nucleotide, guanosine-3',5'-(bis)pyrophospahte (ppGpp). It was proposed recently that ppGpp acts by decreasing stability of open complexes at promoters that make short-lived open complexes, e.g. the rRNA promoters. However, here we report that the bacteriophage lambdap(R) promoter, which forms long-lived open complexes, is inhibited by ppGpp in vitro as observed in vivo. We performed a systematic investigation of the ppGpp-specific inhibition of transcription initiation at lambdap(R) and found that ppGpp does decrease stability of open complexes at lambdap(R), but only slightly. Likewise the equilbrium binding constant and rate of open complex formation by RNA polymerase at lambdap(R) are only slightly affected by ppGpp. The major effect of ppGpp-mediated inhibition is to decrease the rate of promoter escape. We conclude that ppGpp-mediated inhibition of transcription initiation is not restricted to promoters that make short-lived open complexes. Rather we conclude that the initial catalytic step of transcript formation is affected by ppGpp, specifically formation of the first phosphodiester bond is inhibited by ppGpp at) lambdap(R).