Differences of tRNA identity between Escherichia coli and Saccharomyces cerevisiae (yeast).

同源氨基酸- trna合成酶对trna的正确识别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。我们使用体外转录本检测了来自酿酒酵母（酵母）和嗜热热菌的几种tRNA物种的身份元素。对于大肠杆菌、嗜热杆菌和酵母的tRNA^<Thr>，受体茎中的第一个碱基对和反密码子的第二和第三个位置确实被保留为主要的身份元件。然而，在大肠杆菌中，与苏氨酸的氨基酰化需要受体茎中的第二个碱基对C2-G71，而在嗜热t.菌或酵母中则不需要。此外，大肠杆菌中的鉴别碱基A73不参与特异性氨基酰化，而嗜热杆菌中的U73和酵母中的A73有助于tRNA的识别，尽管在突变的数量效应上存在差异。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菌的糖基化很重要，而第三个碱基对对酵母的糖基化很重要。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。

Correct recognition of tRNAs by their cognate aminoacy-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. We examined the identity elements of several tRNA species from Saccharomyces cerevisiae (yeast) and Thermus thermophilus using in vitro transcripts. For E.coli, T.thermophilus and yeast tRNA^<Thr>, the first base pair in the acceptor stem and the second and third positions of the anticodon are indeed retained as major identity elements. However the second base pair, C2-G71, in the acceptor stem is required for aminoacylation with threonine in E.coli, but not in T.thermophilus or yeast. In addition, the discriminator base, A73, in E.coli is not involved in the specific aminoacylation, whereas U73 in T.thermophilus and A73 in yeast contribute to the tRNA identity, although with differences in the quantitative effects on mutations. 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 for 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.