细菌T-box核开关见于编码“氨酰基-tRNA合成酶”（为tRNAs加载氨基酸的酶）的基因的5′ UTR中。它们与其他核开关的不同之处在于，它们结合tRNAs而非一个小分子或代谢物来调控表达。现在，Jinwei Zhang 和 Adrian Ferré-D’Amaré解决了与tRNA 结合在一起的T-box tRNA结合域Stem I的晶体结构。这一人们等待已久的结构显示，该区域不只是结合“反密码子”，而且还支持着整个tRNA，形成一个延伸的界面。“结合”受到在T-box RNA 和 tRNA中的相互“诱导契合”的促进。T-loop主题介导一些相互作用，与RNase P和由大核糖体亚单元构成的一个区域之间的相互作用相似，尽管三个结构并没有一个共同的演化祖先。（生物谷Bioon.com）
生物谷推荐英文摘要：
Nature doi:10.1038/nature12440
Co-crystal structure of a T-box riboswitch stem I domain in complex with its cognate tRNA
Jinwei Zhang & Adrian R. Ferré-D’Amaré
In Gram-positive bacteria, T-box riboswitches regulate the expression of aminoacyl-tRNA synthetases and other proteins in response to fluctuating transfer RNA aminoacylation levels under various nutritional states. T-boxes reside in the 5′-untranslated regions of the messenger RNAs they regulate, and consist of two conserved domains. Stem I contains the specifier trinucleotide that base pairs with the anticodon of cognate tRNA. 3′ to stem I is the antiterminator domain, which base pairs with the tRNA acceptor end and evaluates its aminoacylation state. Despite high phylogenetic conservation and widespread occurrence in pathogens, the structural basis of tRNA recognition by this riboswitch remains ill defined. Here we demonstrate that the ~100-nucleotide T-box stem I is necessary and sufficient for specific, high-affinity (dissociation constant (Kd) ~150nM) tRNA binding, and report the structure of Oceanobacillus iheyensis glyQ stem I in complex with its cognate tRNA at 3.2A resolution. Stem I recognizes the overall architecture of tRNA in addition to its anticodon, something accomplished by large ribonucleoproteins such as the ribosome, or proteins such as aminoacyl-tRNA synthetases5, but is unprecedented for a compact mRNA domain. The C-shaped stem I cradles the L-shaped tRNA, forming an extended (1,6042) intermolecular interface. In addition to the specifier–anticodon interaction, two interdigitated T-loops near the apex of stem I stack on the tRNA elbow in a manner analogous to those of the J11/12–J12/11 motif6 of RNase P and the L1 stalk7 of the ribosomal E-site. Because these ribonucleoproteins and T-boxes are unrelated, this strategy to recognize a universal tRNA feature probably evolved convergently. Mutually induced fit of stem I and the tRNA exploiting the intrinsic flexibility of tRNA and its conserved post-transcriptional modifications results in high shape complementarity, which in addition to providing specificity and affinity, globally organizes the T-box to orchestrate tRNA-dependent transcription regulation.
