tRNAs are the most highly modified RNAs in all cells, and formation of 5-methyluridine (m⁵U) at position 54 in the T arm is a common RNA modification found in all tRNAs. The m⁵U modification is generated by the methyltransferase TrmA. Here, we test and prove the hypothesis that Escherichia coli TrmA has dual functions, acting both as a methyltransferase and as a tRNA chaperone. We identify two conserved residues, F106 and H125, in the RNA-binding domain of TrmA, which interact with the tRNA elbow and are critical for tRNA binding. Co-culture competition assays reveal that the catalytic activity of TrmA is important for cellular fitness, and that substitutions of F106 or H125 impair cellular fitness. We directly show that TrmA enhances tRNA folding in vitro independent of its catalytic activity. In conclusion, our study suggests that F106 and H125 in the RNA-binding domain of TrmA act as a wedge disrupting tertiary interactions between tRNA’s D arm and T arm; this tRNA unfolding is the mechanistic basis for TrmA’s tRNA chaperone activity. TrmA is the second tRNA modifying enzyme next to the pseudouridine synthase TruB shown to act as a tRNA chaperone supporting a functional link between RNA modification and folding.

中文翻译：

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甲基转移酶TrmA通过与其RNA结合域相互作用而促进tRNA折叠。

tRNA是所有细胞中修饰度最高的RNA，在T臂第54位形成5-甲基尿苷（m ⁵ U）是在所有tRNA中常见的RNA修饰。m ⁵ U修饰是由甲基转移酶TrmA产生的。在这里，我们测试并证明了大肠杆菌TrmA具有双重功能的假设，即既充当甲基转移酶又充当tRNA伴侣。我们在TrmA的RNA结合域中鉴定了两个保守残基F106和H125，它们与tRNA肘相互作用，对于tRNA结合至关重要。共培养竞争试验表明，TrmA的催化活性对于细胞适应性很重要，而F106或H125的取代会损害细胞适应性。我们直接表明TrmA增强tRNA折叠在体外与其催化活性无关。总之，我们的研究表明，TrmA的RNA结合域中的F106和H125充当楔形物干扰tRNA的D臂和T臂之间的三级相互作用。这种tRNA的展开是TrmA tRNA伴侣活性的机制基础。TrmA是仅次于伪尿苷合酶TruB的第二种tRNA修饰酶，显示为可支持RNA修饰和折叠之间功能性连接的tRNA伴侣。