Eisenberg S P, Yarus M
J Biol Chem. 1980 Feb 10;255(3):1128-37.
A temperature-sensitive (t.s.) tRNATrp from Escherichia coli has a single base change from the wild type (w.t.) species, which results in the loss of a base pair at the bottom of the CCA stem of the cloverleaf structure. Thermodynamic studies on this t.s. tRNA show that it is more susceptible to denaturation than the w.t. due to a larger change in the entropy of denaturation. Correlated with this thermodynamic result is the finding that the denatured t.s. tRNA's T psi C loop is more susceptible to digestion by T1 RNase, suggesting that it has greater freedom than the corresponding structure on the denatured w.t. molecule. In contrast, the native form of the t.s. tRNATrp is very similar to the w.t. with regard to aminoacylation, T1 RNase susceptibility, and column chromatographic mobility, despite the fact that it necessarily has one less base pair. In addition, the well known denaturation-dependent shift in column chromatographic mobility, which is observed for both the t.s. and w.t. molecules, depends on a modification in the anticodon loop, since tRNATrp lacking that modification does not shift when denatured. Thus, though it is not usually thought to be implicated, denaturation probably affects the conformation of the anticodon loop. The lethal phenotype of the mutant at high temperature, defective attenuation of the tryptophan biosynthetic operon in the mutant, and some aspects of the denatured state are clarified by these findings.
来自大肠杆菌的温度敏感型（t.s.）色氨酸转运RNA（tRNATrp）与野生型（w.t.）相比有一个单碱基变化，这导致其在三叶草结构的CCA茎底部失去一对碱基。对这种t.s. tRNA的热力学研究表明，由于变性熵的变化更大，它比野生型更容易变性。与这一热力学结果相关的是，发现变性的t.s. tRNA的TψC环更容易被T1核糖核酸酶消化，这表明它比变性野生型分子上的相应结构具有更大的自由度。相比之下，t.s. tRNATrp的天然形式在氨基酰化、对T1核糖核酸酶的敏感性和柱色谱迁移率方面与野生型非常相似，尽管它必然少了一对碱基。此外，t.s.和野生型分子都观察到的众所周知的柱色谱迁移率随变性的变化取决于反密码子环的修饰，因为缺乏该修饰的tRNATrp变性时不会发生迁移。因此，尽管通常认为变性与反密码子环的构象无关，但变性可能会影响反密码子环的构象。这些发现阐明了该突变体在高温下的致死表型、突变体中色氨酸生物合成操纵子衰减缺陷以及变性状态的一些方面。
