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首页> 外文期刊>Journal of Molecular Biology >Near Saturation of Ribosomal L7/L12 Binding Sites with Ternary Complexes in Slowly Growing E. coli
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Near Saturation of Ribosomal L7/L12 Binding Sites with Ternary Complexes in Slowly Growing E. coli

机译：在缓慢生长大肠杆菌中，核糖瘤L7 / L12结合位点的近饱和度

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For Escherichia coli growing rapidly in rich medium at 37 degrees C, the doubling time can be as short as similar to 20 min and the average rate of translation (k(trl)) can be as fast as similar to 20 amino acids/s. For slower growth arising from poor nutrient quality or from higher growth osmolality, k(trl) decreases significantly. In earlier work from the Hwa lab, a simplified Michaelis-Menten model suggested that the decrease in k(trl) arises from a shortage of ternary complexes (TCs) under nutrient limitation and from slower diffusion of TCs under high growth osmolality. Here we present a single-molecule tracking study of the diffusion of EF-Tu in E. coli growing with doubling times in the range 62-190 min at 37 degrees C due to nutrient limitation, high growth osmolality, or both. The diffusive properties of EF-Tu remain quantitatively indistinguishable across all growth conditions studied. Dissection of the total population into ribosome -bound and free sub-populations, combined with copy number estimates for EF-Tu and ribosomes, indicates that in all cases similar to 3.7 EF-Tu copies are bound on average to each translating 70S ribosome. Thus, the four L7/L12 binding sites adjacent to the ribosomal A-site in E. coli are essentially saturated with TCs in all conditions, facilitating rapid testing of aminoacyl-tRNAs for a codon match. Evidently, the average translation rate is not limited by either the supply of cognate TCs under nutrient limitation or by the diffusion of free TCs at high osmolality. Some other step or steps must be rate limiting for translation in slow growth. (C) 2019 Elsevier Ltd. All rights reserved.
机译：对于在37摄氏度的富培养基中快速生长的大肠杆菌，倍增时间可以短，与20分钟一样短，平均翻译速率（K（Tr1））可以像20氨基酸一样快。对于营养质量差或较高的生长渗透渗透压，k（TRL）显着降低，显着降低。在HWA实验室的早期工作中，简化的MICHAELIS-MENTen模型表明K（TRL）的降低来自营养限制下的三元复合物（TCS）的短缺，以及在高生长渗透压下的TCS较慢的扩散。在这里，我们提出了EF-TU的扩散的单分子跟踪研究，其在大肠杆菌中，由于营养限制，高生长渗透压，或两者，在37℃下的倍增时间为62-190分钟。 EF-TU的扩散特性在所研究的所有生长条件下定量难以区分。将总人口分析到核糖体 - 核糖和游离子群体，与EF-TU和核糖体的拷贝数估计相结合，表明在所有类似于3.7 EF-TU拷贝的情况下，平均均向每个翻译70s核糖体。因此，与大肠杆菌中的核糖体A-位点相邻的四个L7 / L12结合位点基本上在所有条件下饱和TCS，促进了对密码子匹配的氨基酰基-TrNA的快速测试。显然，平均转换率不受营养素限制的同源TCs的限制或通过游离TCS在高渗透压下的扩散。其他一些步骤或步骤必须在缓慢增长中进行翻译。 （c）2019 Elsevier Ltd.保留所有权利。

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