Lee C P, Mandal N, Dyson M R, RajBhandary U L
Department of Biology, Massachusetts Institute of Technology, Cambridge 02139-4307.
Proc Natl Acad Sci U S A. 1993 Aug 1;90(15):7149-52. doi: 10.1073/pnas.90.15.7149.
For many tRNAs, the discriminator base preceding the CCA sequence at the 3' end is important for aminoacylation. We show that the discriminator base influences the stability of the 1.72 base pair onto which it is stacked. Mutations of the discriminator base from adenosine to cytidine or uridine make the cytidine residue in the C1-G72 base pair of mutant Escherichia coli initiator tRNAs more reactive toward sodium bisulfite, the single-strand-specific reagent. The activity of the enzyme Met-tRNA transformylase toward these and other mutant initiator tRNAs is also consistent with destabilization of the 1.72 base pair in vitro and in vivo. By influencing the strength of the 1.72 base pair, the discriminator base could affect the energetic cost of opening the base pair and modulate the structure of the tRNA near the site of aminoacylation. For some aminoacyl-tRNA synthetases and other proteins that interact with tRNA, these factors could be important for specific recognition and/or formation of the transition state during catalysis.
对于许多转运RNA（tRNA）而言，3'端CCA序列之前的鉴别碱基对氨酰化作用很重要。我们发现，鉴别碱基会影响其所在的1.72碱基对的稳定性。鉴别碱基从腺苷突变为胞嘧啶或尿嘧啶后，突变型大肠杆菌起始tRNA的C1-G72碱基对中的胞嘧啶残基对单链特异性试剂亚硫酸氢钠的反应性增强。在体外和体内，甲硫氨酰-tRNA转甲酰基酶对这些及其他突变起始tRNA的活性也与1.72碱基对的不稳定相一致。通过影响1.72碱基对的强度，鉴别碱基可能会影响打开该碱基对的能量消耗，并调节氨酰化位点附近tRNA的结构。对于一些与tRNA相互作用的氨酰-tRNA合成酶和其他蛋白质来说，这些因素对于催化过程中的特异性识别和/或过渡态的形成可能很重要。
