The unique G3:U70 base pair in the acceptor stem of tRNA^Ala has been shown to be a critical recognition site by alanyl-tRNA synthetase (AlaRS). The base pair resides on one of the arms of the L-shaped structure of tRNA (minihelix) and the genetic code has likely evolved from a primordial tRNA-aaRS (aminoacyl-tRNA synthetase) system. In terms of the evolution of tRNA, incorporation of a G:U base pair in the structure would be important. Here, we found that two independent short hairpin RNAs change their conformation through kissing-loop interactions, finally forming a minihelix-like structure, in which the G3:U70 base pair is incorporated. The RNA system can be properly aminoacylated by the minimal Escherichia coli AlaRS variant with alanylation activity (AlaRS442N). Thus, characteristic structural features produced via kissing-loop interactions may provide important clues into the evolution of RNA.

tRNA ^Ala受体茎中独特的 G3:U70 碱基对已被证明是丙氨酰 tRNA 合成酶 (AlaRS) 的关键识别位点。碱基对位于 tRNA（小螺旋）的 L 形结构的一个臂上，遗传密码很可能是从原始 tRNA-aaRS（氨酰基-tRNA 合成酶）系统进化而来的。就 tRNA 的进化而言，在结构中加入 G:U 碱基对很重要。在这里，我们发现两个独立的短发夹 RNA 通过亲吻环相互作用改变了它们的构象，最终形成了一个类似小螺旋的结构，其中包含了 G3:U70 碱基对。RNA系统可以被最小的大肠杆菌适当地氨酰化具有丙氨酸化活性的 AlaRS 变体 (AlaRS442N)。因此，通过亲吻环相互作用产生的特征结构特征可能为 RNA 的进化提供重要线索。