Growth-Optimized Aminoacyl-tRNA Synthetase Levels Prevent Maximal tRNA Charging
Growth-Optimized Aminoacyl-tRNA Synthetase Levels Prevent Maximal tRNA Charging
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DOI：
10.1016/j.cels.2020.07.005
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发表时间：
2020-08-26
期刊：
影响因子：
9.3
通讯作者：
Li, Gene-Wei
中科院分区：
文献类型：
--
作者：
Parker, Darren J.;Lalanne, Jean-Benoit;Li, Gene-Wei
氨酰-tRNA合成酶（aaRS）在给tRNA充电中起双重作用。它们的酶活性既提供蛋白质合成通量，又降低不带电的tRNA水平。尽管不带电荷的tRNA会对细菌生长产生负面影响，但即使在营养丰富的条件下，大量浓度的tRNA也会保持脱酰化。在这里，我们表明，在枯草芽孢杆菌中的tRNA充电没有最大化，由于在快速生长过程中的阿尔斯生产的优化，这优先要求在蛋白质合成充电水平。通过精确调节的翻译动力学和严格响应来减轻不带电荷的tRNA的存在，两者对阿尔斯过量生产不敏感，但对生产不足反应强烈，允许刚好足够的阿尔斯生产在“适合度悬崖”之上。“值得注意的是，我们发现，即使没有外部饥饿，严格的反应也可以减轻所有阿尔斯生产不足水平的适应性缺陷，因此，坚持最小的，满足通量的蛋白质生产驱动有限的tRNA充电，并为集成生长控制网络的灵敏度和设定点提供基础。
Aminoacyl-tRNA synthetases (aaRSs) serve a dual role in charging tRNAs. Their enzymatic activities both provide protein synthesis flux and reduce uncharged tRNA levels. Although uncharged tRNAs can negatively impact bacterial growth, substantial concentrations of tRNAs remain deacylated even under nutrient-rich conditions. Here, we show that tRNA charging in Bacillus subtilis is not maximized due to optimization of aaRS production during rapid growth, which prioritizes demands in protein synthesis over charging levels. The presence of uncharged tRNAs is alleviated by precisely tuned translation kinetics and the stringent response, both insensitive to aaRS overproduction but sharply responsive to underproduction, allowing for just enough aaRS production atop a "fitness cliff." Notably, we find that the stringent response mitigates fitness defects at all aaRS underproduction levels even without external starvation, Thus, adherence to minimal, flux-satisfying protein production drives limited tRNA charging and provides a basis for the sensitivity and setpoints of an integrated growth-control network.