Zhouravleva G, Frolova L, Le Goff X, Le Guellec R, Inge-Vechtomov S, Kisselev L, Philippe M
Département de Biologie et Génétique du Développement, CNRS URA 256, Université de Rennes, France.
EMBO J. 1995 Aug 15;14(16):4065-72. doi: 10.1002/j.1460-2075.1995.tb00078.x.
Termination of translation in higher organisms is a GTP-dependent process. However, in the structure of the single polypeptide chain release factor known so far (eRF1) there are no GTP binding motifs. Moreover, in prokaryotes, a GTP binding protein, RF3, stimulates translation termination. From these observations we proposed that a second eRF should exist, conferring GTP dependence for translation termination. Here, we have shown that the newly sequenced GTP binding Sup35-like protein from Xenopus laevis, termed eRF3, exhibits in vitro three important functional properties: (i) although being inactive as an eRF on its own, it greatly stimulates eRF1 activity in the presence of GTP and low concentrations of stop codons, resembling the properties of prokaryotic RF3; (ii) it binds and probably hydrolyses GTP; and (iii) it binds to eRF1. The structure of the C-domain of the X.laevis eRF3 protein is highly conserved with other Sup35-like proteins, as was also shown earlier for the eRF1 protein family. From these and our previous data, we propose that yeast Sup45 and Sup35 proteins belonging to eRF1 and eRF3 protein families respectively are also yeast termination factors. The absence of structural resemblance of eRF1 and eRF3 to prokaryotic RF1/2 and RF3 respectively, may point to the different evolutionary origin of the translation termination machinery in eukaryotes and prokaryotes. It is proposed that a quaternary complex composed of eRF1, eRF3, GTP and a stop codon of the mRNA is involved in termination of polypeptide synthesis in ribosomes.
高等生物中翻译的终止是一个依赖GTP的过程。然而，在目前所知的单一多肽链释放因子（eRF1）的结构中，没有GTP结合基序。此外，在原核生物中，一种GTP结合蛋白RF3可刺激翻译终止。基于这些观察结果，我们推测应该存在第二种eRF，它赋予翻译终止对GTP的依赖性。在此，我们已表明，从非洲爪蟾新测序的GTP结合Sup35样蛋白，称为eRF3，在体外表现出三个重要的功能特性：（i）尽管其自身作为eRF无活性，但在存在GTP和低浓度终止密码子的情况下，它能极大地刺激eRF1的活性，类似于原核生物RF3的特性；（ii）它结合并可能水解GTP；以及（iii）它与eRF1结合。非洲爪蟾eRF3蛋白C结构域的结构与其他Sup35样蛋白高度保守，这一点之前对eRF1蛋白家族也有显示。基于这些以及我们之前的数据，我们推测分别属于eRF1和eRF3蛋白家族的酵母Sup45和Sup35蛋白也是酵母终止因子。eRF1和eRF3分别与原核生物的RF1/2和RF3在结构上缺乏相似性，这可能表明真核生物和原核生物翻译终止机制有不同的进化起源。有人提出，由eRF1、eRF3、GTP和mRNA的终止密码子组成的四元复合物参与核糖体中多肽合成的终止。
