Delayed-relaxed response explained by hyperactivation of RelE
Delayed-relaxed response explained by hyperactivation of RelE
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DOI：
10.1111/j.1365-2958.2004.04127.x
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发表时间：
2004-07-01
影响因子：
3.6
通讯作者：
Gerdes, K
中科院分区：
文献类型：
--
作者：
Christensen, SK;Gerdes, K
大肠杆菌编码两个rel基因座，这两个基因座在氨基酸饥饿期间都有助于控制大分子的合成。relA （ppGpp合成酶I）的产物负责合成四磷酸鸟苷ppGpp，这是一种严格控制稳定RNA合成的信号分子。第二个rel基因座relBE是通过relB突变确定的，relB突变赋予了所谓的“延迟放松反应”，其特征是在氨基酸饥饿开始后大约10分钟的滞后期后继续进行RNA合成。我们在这里表明延迟放松反应是过度激活RelE的结果。与野生型细胞一样，饥饿开始后，relB101 relE细胞中的[ppGpp]急剧增加，但迅速恢复到饥饿前的水平。RelE是一种全球性的翻译抑制剂，通过蛋白与蛋白的直接相互作用被RelB中和。在氨基酸饥饿过程中，Lon蛋白酶通过降解RelB激活RelE。我们发现relB的突变赋予延迟放松表型使relB不稳定。这些突变在氨基酸饥饿期间导致严重的RelE依赖性翻译抑制，表明RelE过度激活。通过测量RelE介导的tmRNA的切割，直接显示了氨基酸饥饿期间RelE的过度激活。rele介导的翻译关闭终止了氨基酸消耗，并解释了在relB突变细胞中观察到的ppGpp水平的快速恢复。恢复饥饿前的ppGpp水平，反过来，允许恢复在延迟放松反应期间看到的稳定RNA合成。
Escherichia coli encodes two rel loci, both of which contribute to the control of synthesis of macromolecules during amino acid starvation. The product of relA (ppGpp synthetase I) is responsible for the synthesis of guanosine tetraphosphate, ppGpp, the signal molecule that exerts stringent control of stable RNA synthesis. The second rel locus, relBE, was identified by mutations in relB that confer a so-called 'delayed-relaxed response' characterized by continued RNA synthesis after a lag period of approximate to 10 min after the onset of amino acid starvation. We show here that the delayed-relaxed response is a consequence of hyperactivation of RelE. As in wild-type cells, [ppGpp] increased sharply in relB101 relE cells after the onset of starvation, but returned rapidly to the prestarvation level. RelE is a global inhibitor of translation that is neutralized by RelB by direct protein-protein interaction. Lon protease activates RelE during amino acid starvation by degradation of RelB. We found that mutations in relB that conferred the delayed-relaxed phenotype destabilized RelB. Such mutations confer severe RelE-dependent inhibition of translation during amino acid starvation, indicating hyperactivation of RelE. Hyperactivation of RelE during amino acid starvation was shown directly by measurement of RelE-mediated cleavage of tmRNA. The RelE-mediated shutdown of translation terminated amino acid consumption and explains the rapid restoration of the ppGpp level observed in relB mutant cells. Restoration of the prestarvation level of ppGpp, in turn, allows for the resumption of stable RNA synthesis seen during the delayed-relaxed response.