Menez J, Heurgué-Hamard V, Buckingham R H
UPR9073 du CNRS, Institut de Biologie Physico-Chimique, 13 rue Pierre et Marie Curie, F-75005 Paris, France.
Nucleic Acids Res. 2000 Dec 1;28(23):4725-32. doi: 10.1093/nar/28.23.4725.
High-level expression of non-functional model proteins, derived from elongation factor EF-Tu by the deletion of an essential domain, greatly inhibits the growth of Escherichia coli partly deficient in peptidyl-tRNA hydrolase. High-level expression in wild-type cells has little effect on growth. The inhibitory effect is therefore presumably due to the sequestration of essential tRNA species, partly in the form of free peptidyl-tRNA. The growth inhibitory effect can be modulated by changing the last sense codon in the genes encoding the model proteins. Thus, replacement of Ser by Lys or His at this position increases growth inhibition. The effects of 11 changes studied are related to the rates of accumulation previously observed of the corresponding families of peptidyl-tRNA. Two non-exclusive hypotheses are proposed to account for these observations: first, the last sense codon of mRNA is a preferred site of peptidyl-tRNA drop-off in cells, due to the slow rate of translation termination compared with sense codon translation; secondly, the relatively long pause of the ribosome at the stop codon (of the order of 1 s), results in significant temporary sequestration on the ribosome of the tRNA cognate to the last sense codon.
通过缺失一个必需结构域从延伸因子EF-Tu衍生而来的无功能模型蛋白的高水平表达，极大地抑制了肽基-tRNA水解酶部分缺陷的大肠杆菌的生长。在野生型细胞中的高水平表达对生长影响很小。因此，抑制作用可能是由于必需tRNA种类的隔离，部分以游离肽基-tRNA的形式存在。通过改变编码模型蛋白的基因中的最后一个有义密码子，可以调节生长抑制作用。因此，在这个位置将Ser替换为Lys或His会增加生长抑制。所研究的11种变化的影响与先前观察到的相应肽基-tRNA家族的积累速率有关。提出了两个非排他性假说来解释这些观察结果：第一，由于与有义密码子翻译相比翻译终止速率较慢，mRNA的最后一个有义密码子是细胞中肽基-tRNA脱落的首选位点；第二，核糖体在终止密码子处相对较长的停顿（约1秒）导致与最后一个有义密码子同源的tRNA在核糖体上的显著暂时隔离。
