DksA potentiates direct activation of amino acid promoters by ppGpp
DksA potentiates direct activation of amino acid promoters by ppGpp
复制标题
DOI：
10.1073/pnas.0501170102
复制
发表时间：
2005-05-31
影响因子：
11.1
通讯作者：
Gourse, RL
中科院分区：
文献类型：
--
作者：
Paul, BJ;Berkmen, MB;Gourse, RL
在大肠杆菌中，氨基酸饥饿导致一系列基因表达的变化，包括rRNA和tRNA启动子的抑制和某些氨基酸生物合成和运输的启动子的激活。异常核苷酸ppGpp在正负向调控中都发挥着重要作用。此前，我们和其他人认为ppGpp的积极作用可能是间接的，原因是抑制了rRNA转录，从而释放了RNA聚合酶与其他启动子结合。最近，我们发现DksA与RNA聚合酶结合，大大增强了ppGpp对rRNA启动子负调控的直接作用。这一结论促使我们重新评估ppGpp是否也可能在积极对照中起到直接作用。我们在这里表明，ppGpp极大地提高了纯化系统中氨基酸启动子的转录启动速度，但只有在Dks A存在的情况下。激活是通过刺激打开络合物形成途径上的异构化步骤的速度进行的。与ppGpp/Dks A在体内直接和间接刺激氨基酸启动子的模型一致，缺乏dks A的细胞在氨基酸饥饿后无法激活hisG启动子的转录。我们的结果说明了转录因子如何在不结合DNA的情况下正向调节转录启动，证明了除了对rRNA的影响外，dks A还直接影响启动子，并表明以前与dks A相关的一些多效性效应可能归因于dks A对参与多种细胞功能的启动子的直接影响。
Amino acid starvation in Escherichia coli results in a spectrum of changes in gene expression, including inhibition of rRNA and tRNA promoters and activation of certain promoters for amino acid biosynthesis and transport. The unusual nucleotide ppGpp plays an important role in both negative and positive regulation. Previously, we and others suggested that positive effects of ppGpp might be indirect, resulting from the inhibition of rRNA transcription and, thus, liberation of RNA polymerase for binding to other promoters. Recently, we showed that DksA binds to RNA polymerase and greatly enhances direct effects of ppGpp on the negative control of rRNA promoters. This conclusion prompted us to re-evaluate whether ppGpp might also have a direct role in positive control. We show here that ppGpp greatly increases the rate of transcription initiation from amino acid promoters in a purified system but only when DksA is present. Activation occurs by stimulation of the rate of an isomerization step on the pathway to open complex formation. Consistent with the model that ppGpp/DksA stimulates amino acid promoters both directly and indirectly in vivo, cells lacking dksA fail to activate transcription from the hisG promoter after amino acid starvation. Our results illustrate how transcription factors can positively regulate transcription initiation without binding DNA, demonstrate that dksA directly affects promoters in addition to those for rRNA, and suggest that some of the pleiotropic effects previously associated with dksA might be ascribable to direct effects of dksA on promoters involved in a wide variety of cellular functions.