Hanada T, Suzuki T, Yokogawa T, Takemoto-Hori C, Sprinzl M, Watanabe K
Department of Chemistry and Biotechnology, Graduate School of Engineering, The University of Tokyo 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656, Japan.
Genes Cells. 2001 Dec;6(12):1019-30. doi: 10.1046/j.1365-2443.2001.00491.x.
Metazoan mitochondrial (mt) tRNAs are structurally quite different from the canonical cloverleaf secondary structure. The mammalian mt tRNASerGCU for AGY codons (Y = C or U) lacks the entire D arm, whereas tRNASerUGA for UCN codons (N = A, G, C or U) has an extended anti-codon stem. It has been a long-standing problem to prove experimentally how these tRNAsSer work in the mt translation system.
To solve the above-mentioned problem, we examined their translational abilities in an in vitro bovine mitochondrial translation system using transcripts of altered tRNASer analogues derived from bovine mitochondria. Both tRNASer analogues had almost the same ability to form ternary complexes with mt EF-Tu and GTP. The D-arm-lacking tRNASer GCU analogue had considerably lower translational activity than the tRNASerUGA analogue and produced mostly short oligopeptides, up to a tetramer. In addition, tRNASerGCU analogue was disfavoured by the ribosome when other tRNAs capable of decoding the cognate codon were available.
Both mt tRNASerGCU and tRNASerUGA analogues with unusual secondary structure were found to be capable of translation on the ribosome. However, the tRNASerGCU analogue has some molecular disadvantage on the ribosome, which probably derives from the lack of a D arm.
后生动物线粒体（mt）tRNA在结构上与典型的三叶草二级结构有很大不同。用于AGY密码子（Y = C或U）的哺乳动物mt tRNASerGCU缺少整个D臂，而用于UCN密码子（N = A、G、C或U）的tRNASerUGA具有延长的反密码子茎。通过实验证明这些tRNASer在mt翻译系统中如何发挥作用一直是个长期存在的问题。
为了解决上述问题，我们在体外牛线粒体翻译系统中使用源自牛线粒体的改变后的tRNASer类似物转录本研究了它们的翻译能力。两种tRNASer类似物与mt EF-Tu和GTP形成三元复合物的能力几乎相同。缺少D臂的tRNASer GCU类似物的翻译活性明显低于tRNASerUGA类似物，并且主要产生短的寡肽，最长为四聚体。此外，当有其他能够解码同源密码子的tRNA时，核糖体不青睐tRNASerGCU类似物。
发现具有异常二级结构的mt tRNASerGCU和tRNASerUGA类似物都能够在核糖体上进行翻译。然而，tRNASerGCU类似物在核糖体上存在一些分子劣势，这可能源于缺少D臂。
