ppGpp is the major source of growth rate control in E. coli.
ppGpp is the major source of growth rate control in E. coli.
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DOI：
10.1111/j.1462-2920.2010.02357.x
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发表时间：
2011-03
影响因子：
5.1
通讯作者：
Cashel M
中科院分区：
文献类型：
--
作者：
Potrykus K;Murphy H;Philippe N;Cashel M
人们普遍认为，肠杆菌科的DNA、RNA和蛋白质含量是作为指数生长速率的函数进行调节的；无论生长培养基的具体成分如何，大分子含量都会随着生长速度的加快而增加。这种被称为生长速率控制的现象主要涉及核糖体RNA和核糖体蛋白质合成的调节。然而，全局调节因子ppGpp是否是生长速率控制的主要决定因素尚不确定。因此，在此我们重新评估了在特定培养基中不同平衡生长速率下ppGpp对大分子含量的影响。我们发现，当不存在ppGpp时，快速生长和缓慢生长的细胞中RNA/蛋白质和RNA/DNA的比率是相等的。此外，RNA含量增加的生长缓慢的ppGpp缺陷细胞，其核糖体亚基组成正常，尽管与快速生长的野生型细胞相比多聚核糖体含量降低。由此我们得出结论，在没有ppGpp的情况下不会发生生长速率控制。此外，在ppGpp缺陷细胞中人为提高ppGpp水平或引入严格的RNA聚合酶突变体可恢复这种控制。我们认为这些发现有力地支持了ppGpp的作用，并反驳了大肠杆菌和其他肠道细菌中其他因素对生长速率控制的冗余调节。
It is widely accepted that the DNA, RNA and protein content of Enterobacteriaceae is regulated as a function of exponential growth rates; macromolecular content increases with faster growth regardless of specific composition of the growth medium. This phenomenon, called growth rate control, primarily involves regulation of ribosomal RNA and ribosomal protein synthesis. However, it was uncertain whether the global regulator ppGpp is the major determinant for growth rate control. Therefore, here we re-evaluate the effect of ppGpp on macromolecular content for different balanced growth rates in defined media. We find that when ppGpp is absent RNA/protein and RNA/DNA ratios are equivalent in fast and slow growing cells. Moreover, slow growing ppGpp deficient cells with increased RNA content, display a normal ribosomal subunit composition although polysome content is reduced when compared to fast growing wild type cells. From this we conclude that growth rate control does not occur in the absence of ppGpp. Also, artificial elevation of ppGpp or introduction of stringent RNA polymerase mutants in ppGpp deficient cells restores this control. We believe these findings strongly argue in favor of ppGpp and against redundant regulation of growth rate control by other factors in E. coli and other enteric bacteria.