Let‐7 is an evolutionary conserved microRNA that mediates post‐transcriptional gene silencing to regulate a wide range of biological processes, including development, differentiation, and tumor suppression. Let‐7 biogenesis is tightly regulated by several RNA‐binding proteins, including Lin28A/B, which represses let‐7 maturation. To identify new regulators of let‐7, we devised a cell‐based functional screen of RNA‐binding proteins using a let‐7 sensor luciferase reporter and identified the tRNA pseudouridine synthase, TruB1. TruB1 enhanced maturation specifically of let‐7 family members. Rather than inducing pseudouridylation of the miRNAs, high‐throughput sequencing crosslinking immunoprecipitation (HITS‐CLIP) and biochemical analyses revealed direct binding between endogenous TruB1 and the stem‐loop structure of pri‐let‐7, which also binds Lin28A/B. TruB1 selectively enhanced the interaction between pri‐let‐7 and the microprocessor DGCR8, which mediates miRNA maturation. Finally, TruB1 suppressed cell proliferation, which was mediated in part by let‐7. Altogether, we reveal an unexpected function for TruB1 in promoting let‐7 maturation.

中文翻译：

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tRNA 假尿苷合酶 TruB1 调节 let-7 miRNA 的成熟。

Let-7 是一种进化保守的 microRNA，可介导转录后基因沉默，从而调节广泛的生物过程，包括发育、分化和肿瘤抑制。Let-7 的生物发生受到多种 RNA 结合蛋白的严格调控，包括抑制 let-7 成熟的 Lin28A/B。为了鉴定 let-7 的新调节因子，我们使用 let-7 传感器荧光素酶报告基因设计了一种基于细胞的 RNA 结合蛋白功能筛选，并鉴定了 tRNA 假尿苷合酶 TruB1。TruB1 特别促进了 let-7 家族成员的成熟。高通量测序交联免疫沉淀 (HITS-CLIP) 和生化分析揭示了内源性 TruB1 与 pri-let-7 的茎环结构之间的直接结合，而 pri-let-7 也结合了 Lin28A/B，而不是诱导 miRNA 的假尿苷化。TruB1 选择性增强 pri-let-7 和微处理器 DGCR8 之间的相互作用，从而介导 miRNA 成熟。最后，TruB1 抑制细胞增殖，这部分是由 let-7 介导的。总而言之，我们揭示了 TruB1 在促进 let-7 成熟方面的意外功能。