Evolution of tRNA Identity.

同源的氨基酰基- trna合成酶正确识别trna对于维持准确翻译至关重要。为了从具有相似l型三级结构的各种tRNA物种中区分同源tRNA，氨基酰基tRNA合成酶被发现识别相对少量的tRNA核苷酸，其中通常包括反密码子核苷酸和73位的鉴别碱基。尽管最近对其他生物体进行了一些研究，但大多数现有数据都偏向于大肠杆菌系统。对于甘氨酸trna，鉴别碱基，受体茎中的第二碱基对，以及反密码子核苷酸C35和C36，有助于所有三种甘氨酸- trna合成酶的特异性糖基化，鉴别碱基在原核生物（U73）和真核生物（A73）之间有所不同。第一个碱基对G1-C72对大肠杆菌和嗜热t菌的糖基化起重要作用，而第三个碱基对酵母的糖基化起重要作用。上述结果表明，虽然主要的同一性元素在整个进化过程中都是保守的，但氨基酰基trna合成酶识别底物的机制似乎在不同物种之间有所不同。在大肠杆菌系统中，苏氨酸tRNA的鉴别碱基（A73）不参与苏氨酸-tRNA合成酶（ThrRS）的苏氨酸化活性。为了研究这个古细菌苏氨酸tRNA鉴别碱基在ThrRS苏氨酸基化中的作用，我们研究了大肠杆菌、嗜盐古菌（Haloferax volcanii）和极端嗜热古菌（Aeropyrum pernix）之间的跨种氨基酰化反应。结果发现，大肠杆菌ThrRS可使古细菌苏氨酸tRNA氨基化（U73），而大肠杆菌苏氨酸tRNA不被古细菌ThrRS氨基化。利用大肠杆菌苏氨酸tRNA体外突变体进行苏氨酸化实验的结果表明，只有含有U73的突变体苏氨酸tRNA被苏氨酸化。这些结果表明苏氨酸tRNA的鉴别碱基U73是古菌ThrRS识别苏氨酸的重要决定因素。少

Correct recognition of tRNAs by their cognate aminoacyl-tRNA synthetases is essential to the maintenance of accurate translation. To discriminate the cognate tRNA from a pool of various tRNA species sharing a similar L-shaped tertiary structure, the aminoacyl-tRNA synthetase was found to recognize a relatively small number of nucleotides of the tRNA, which offen include the anticodon nucleotides and the discriminator base at position 73. Most of the available data are biased to the Escherichia coli system, although a few studies in other organisms have recently been made.In case of glycine tRNAs, discriminator base, the second base pair in the acceptor stem, and the anticodon nuclotides, C35 and C36, contribute to the specific glycylation of all three glycly-tRNA synthetases, the discriminator base differing between prokaryotes (U73) and eukaryote (A73). The first base pair, G1-C72, is important for glycylation in E. coli and T. thermophilus, whereas the third base pair is important fo … More r glycylation in yeast. These above results indicate that while major identity elements have been conserved throughout evolution, the mechanism by which aminoacyl-tRNA synthetases recognize their substrates seems to have diverged somewhat among different species.In the E. coli system, the discriminator base of threonine tRNA (A73) is not involved in the threonylation activity by threonyl-tRNA synthetase (ThrRS). To investigate the contribution of this discriminator base of archaea threonine tRNA in threonylation by ThrRS, cross-species aminoacylation reactions among E. coli, Haloferax volcanii (halophilic archae), and Aeropyrum pernix (extreme thermophilic archaea) have been studied. It was found that E. coli ThrRS threonylated the archaea threonine tRNAs (U73), but E. coli threonine tRNA was not aminoacylated by archaea ThrRS. Results of the threonylation experiment using in vitro mutants of E. coli threonine tRNA showed that only the mutant threonine tRNA having U73 was threonylated. These findings indicate that the discriminator base U73 of threonine tRNA is a strong determinant for the recognition by archaea ThrRS. Less