Bonne Zh, Kern D, Ebel' Zh P
Mol Biol (Mosk). 1975 Jan-Feb;9(1):48-54.
A few examples of incorrect interactions between aminoacyl-tRNA-synthetases and tRNAs extracted from the same organism have already been demonstrated. These interactions can lead, in most cases, to incorrect aminoacylations. The lack of specificity of the aminoacyl-tRNA suggests that incorrect interactions could be a general phenomenon. The aim of this study is to check whether incorrect interactions are a general feature, i.e. whether every aminoacyl-tTNA-synthetase is able to interact with homologous non-cognate tRNAs. In that case, it is interesting to know whether a given aminoacyl-tRNA-synthetase is able to recognize any tRNA or only a particular group of tRNAs. The existence of such groups would lead to the concept of tRNA families. For that, we estimated the affinities of non-cognate homologous tRNA species for yeast valyl-tRNA-synthetase by using competition experiments. The measured affinities varied, in standard aminoacylation conditions, between 1:100 to 1:1000 of that of the non-cognate tRNA. In the absence of Mg2+ ions or in the presence of low concentration of this cation, the affinities were higher and could reach 1:3 of the affinity of the cognate tRNA. On the other hand, we determined the inhibitory effect of a high concentration of tRNAVal toward the aminoacylation of tRNAs specific for 13 amino acids. In order to compare the effects, we determined approximate Km/Ki values. These values ranged from 0.07 for methionyl tRNA synthetase to 0.002 for leucyl tRNA synthetase. For some aminoacyl-tRNA-synthetases, the inhibition was too low to be detected by this technique. Two conclusions arise from this study. First, it seems that non-specific recognitions are quite a general phenomenon. Secondly, if one classifies tTNAs according to their affinities for valyl-tRNA-synthetase, it does not appear any well cut group of tRNAs. This result is not conflicting with the fact that on the basis of aminoacylation criteria several authors have found tRNA and aminoacyl-tRNA-synthetase families since we have already shown that discrimination depends rather on the maximal velocity of the reaction than on the affinity between the tRNA and the aminoacyl-tRNA-synthetases. Finally, the non-existence of clear-cut recognition families of tRNAs casts some doubts on the approach consisting in the characterisation of recognition sites of the tRNAs by the aminoacyl-tRNA-synthetases by comparing the sequences of tRNAs which are amonoacylated by a given aminoacyl-tRNA-synthetase.
已经证实了同一生物体中提取的氨酰 - tRNA合成酶与tRNA之间存在一些错误相互作用的例子。在大多数情况下，这些相互作用会导致错误的氨酰化。氨酰 - tRNA缺乏特异性表明错误相互作用可能是一种普遍现象。本研究的目的是检验错误相互作用是否是一个普遍特征，即是否每种氨酰 - tRNA合成酶都能够与同源的非对应tRNA相互作用。在这种情况下，了解特定的氨酰 - tRNA合成酶是能够识别任何tRNA还是仅识别特定的一组tRNA是很有趣的。这样的组的存在将引出tRNA家族的概念。为此，我们通过竞争实验估计了非对应同源tRNA种类与酵母缬氨酰 - tRNA合成酶的亲和力。在标准氨酰化条件下，测得的亲和力在非对应tRNA的1:100至1:1000之间变化。在没有Mg2 +离子或存在低浓度该阳离子的情况下，亲和力更高，可达到对应tRNA亲和力的1:3。另一方面，我们确定了当高浓度的tRNAVal对13种氨基酸特异性的tRNA的氨酰化的抑制作用。为了比较这些作用，我们确定了近似的Km / Ki值。这些值范围从甲硫氨酰tRNA合成酶的0.07到亮氨酰tRNA合成酶的0.002。对于一些氨酰 - tRNA合成酶，抑制作用太低以至于无法通过该技术检测到。这项研究得出两个结论。首先，似乎非特异性识别是一种相当普遍的现象。其次，如果根据tRNA对缬氨酰 - tRNA合成酶的亲和力对tRNA进行分类，似乎没有明显区分的tRNA组。这一结果与一些作者基于氨酰化标准发现tRNA和氨酰 - tRNA合成酶家族这一事实并不矛盾，因为我们已经表明区分更多地取决于反应的最大速度而不是tRNA与氨酰 - tRNA合成酶之间的亲和力。最后，不存在明确的tRNA识别家族这一情况对通过比较由给定氨酰 - tRNA合成酶进行氨酰化的tRNA序列来表征tRNA识别位点的方法提出了一些质疑。
