Yokoyama S, Watanabe K, Miyazawa T
Department of Biophysics and Biochemistry, Faculty of Science, University of Tokyo, Japan.
Adv Biophys. 1987;23:115-47. doi: 10.1016/0065-227x(87)90006-2.
tRNA species from an extreme thermophile T. thermophilus that grows up to 85 degrees C have been found to be more thermostable than those from moderate thermophiles and mesophiles. Such thermostability of T. thermophilus tRNA species is partly due to the high contents of G.C base pairs in the stem regions. In addition, a novel modified nucleoside s2T has been found that substitutes T in position 54. The extent of 2-thiolation of T(54) has been found to depend on environmental temperatures from 50 to 80 degrees C. Two tRNA(Ile) species have been isolated from T. thermophilus HB8, tRNA(1aIle) with s2T(54) and tRNA(1bIle) with T(54), which have the identical nucleotide sequence except for position 54. However, the melting temperature of tRNA(1aIle) is higher by 3 degrees C than that of tRNA(1bIle). This clearly indicates that the 2-thiolation of T(54) contributes directly to the thermostability of T. thermophilus tRNA species. Proton NMR analyses have shown that the nucleoside s2T is "rigid" and predominantly takes the C3'-endo-gg-anti form of A-RNA, because of the steric effect of the bulky 2-thiocarbonyl groups and the 2'-hydroxyl group. Thus, the inherent rigidity of s2T in position 54 significantly enhances the stability of the tertiary structure of tRNA. In protein synthesis of T. thermophilus, s2T(54)-bearing tRNA and T(54)-bearing tRNA species are selectively utilized depending on environmental temperature. In the anticodons of major tRNA species from T. thermophilus, G or C exclusively appears in the first position, and GGN and CCN are favored over synonymous GCN or CGN. These characteristic anticodon sequences correspond to the characteristic codon usage in thermophile genes.
已发现来自最高能在85摄氏度生长的嗜热栖热菌这种极端嗜热菌的tRNA种类比来自中度嗜热菌和嗜温菌的tRNA种类更具热稳定性。嗜热栖热菌tRNA种类的这种热稳定性部分归因于茎区中G.C碱基对的高含量。此外，还发现了一种新型修饰核苷s2T，它取代了第54位的T。已发现T(54)的2-硫醇化程度取决于50至80摄氏度的环境温度。已从嗜热栖热菌HB8中分离出两种tRNA(Ile)种类，带有s2T(54)的tRNA(1aIle)和带有T(54)的tRNA(1bIle)，除了第54位外，它们具有相同的核苷酸序列。然而，tRNA(1aIle)的解链温度比tRNA(1bIle)高3摄氏度。这清楚地表明T(54)的2-硫醇化直接有助于嗜热栖热菌tRNA种类的热稳定性。质子核磁共振分析表明，由于庞大的2-硫羰基基团和2'-羟基的空间效应，核苷s2T是“刚性的”，主要采取A-RNA的C3'-endo-gg-anti形式。因此，第54位s2T的固有刚性显著增强了tRNA三级结构的稳定性。在嗜热栖热菌的蛋白质合成中，根据环境温度选择性地利用带有s2T(54)的tRNA和带有T(54)的tRNA种类。在嗜热栖热菌主要tRNA种类的反密码子中，G或C仅出现在第一位，并且GGN和CCN比同义的GCN或CGN更受青睐。这些特征性的反密码子序列与嗜热菌基因中的特征性密码子使用相对应。
