mRNA association by aminoacyl tRNA synthetase occurs at a putative anticodon mimic and autoregulates translation in response to tRNA levels

Aminoacyl-tRNA synthetases (aaRSs) are well studied for their role in binding and charging tRNAs with cognate amino acids. Recent RNA interactome studies had suggested that these enzymes can also bind polyadenylated RNAs. Here, we explored the mRNA repertoire bound by several yeast aaRSs. RNA immunoprecipitation (RIP) followed by deep sequencing revealed unique sets of mRNAs bound by each aaRS. Interestingly, for every tested aaRSs, a preferential association with its own mRNA was observed, suggesting an autoregulatory process. Self-association of histidyl-tRNA synthetase (HisRS) was found to be mediated primarily through binding to a region predicted to fold into a tRNAHis anticodon-like structure. Introducing point mutations that are expected to disassemble this putative anticodon mimic alleviated self-association, concomitant with increased synthesis of the protein. Finally, we found that increased cellular levels of uncharged tRNAHis lead to reduced self-association and increased HisRS translation, in a manner that depends on the anticodon-like element. Together, these results reveal a novel post-transcriptional autoregulatory mechanism that exploits binding mimicry to control mRNA translation according to tRNA demands.

氨酰-tRNA合成酶（Aminoacyl-tRNA synthetases, aaRSs）因其在结合同源氨基酸并为转运RNA（tRNA）加载对应氨基酸的功能中得到广泛研究而备受关注。近期的RNA相互作用组研究表明，这类酶还可结合聚腺苷酸化RNA。本研究针对数种酵母氨酰-tRNA合成酶所结合的信使RNA（mRNA）全集展开了系统探索。通过RNA免疫共沉淀（RNA immunoprecipitation, RIP）联合深度测序技术，我们发现每种氨酰-tRNA合成酶均结合独特的信使RNA集合。有趣的是，在所有受试的氨酰-tRNA合成酶中，均观察到其与自身编码的mRNA存在优先结合现象，这提示存在一种自我调控过程。研究显示，组氨酰-tRNA合成酶（histidyl-tRNA synthetase, HisRS）的自身相互作用，主要通过结合一段被预测可折叠为tRNA^His反密码子样结构的区域所介导。引入可破坏该推定反密码子模拟结构的点突变，可缓解自身相互作用，同时伴随该蛋白合成水平的提升。最后，本研究发现，细胞内未加载氨基酸的tRNA^His水平升高，可通过依赖该反密码子样元件的方式，降低自身相互作用并提升HisRS的翻译效率。综上，本研究揭示了一种全新的转录后自我调控机制：该机制通过结合拟态现象，根据细胞内tRNA的需求精准调控mRNA的翻译过程。