Abstract：
Let-7 was one of the first microRNAs (miRNAs) to be discovered and its expression promotes differentiation during development and function as tumor suppressors in various cancers. The maturation process of let-7 miRNA is tightly regulated by multiple RNA-binding proteins. For example, LIN28 binds to the terminal loops of the precursors of let-7 family and block their processing into mature miRNAs. Trim25 promotes the uridylation-mediated degradation of pre-let-7 modified by LIN28/TUT4. Recently, human pseudouridine synthase TruB1 has been reported to facilitate let-7 maturation by directly binding to pri-let-7 and recruiting Drosha-DGCR8 microprocessor. Through biochemical assay and structural investigation, we show that human TruB1 binds specifically the terminal loop of pri-let-7a1 at nucleotides 31-41, which folds as a small stem-loop architecture. Although TruB1 recognizes the terminal loop of pri-let-7a1 in a way similar to how E. coli TruB interacts with tRNA, a conserved KRKK motif in human and other higher eukaryotes adds an extra binding interface and strengthens the recognition of TruB1 for pri-let-7a1 through electrostatic interactions. These findings reveal the structural basis of TruB1-pri-let-7 interaction which may assists the elucidation of precise role of TruB1 in biogenesis of let-7.
摘要：
Let-7是最早被发现的microRNAs（miRNAs）之一，其表达在发育过程中促进分化，并在各种癌症中作为肿瘤抑制因子发挥作用。let-7miRNA的成熟过程受到多种RNA结合蛋白的严格调控。例如,LIN28与let-7家族前体的末端环结合并阻断它们加工成成熟miRNA。Trim25促进由LIN28/TUT4修饰的pre-let-7的尿苷化介导的降解。最近,据报道，人假尿苷合酶TruB1通过直接与pri-let-7结合并招募Drosha-DGCR8微处理器来促进let-7成熟。通过生化分析和结构研究，我们显示人TruB1在核苷酸31-41处特异性结合pri-let-7a1的末端环，该末端环折叠为小的茎环结构。尽管TruB1以类似于大肠杆菌TruB与tRNA相互作用的方式识别pri-let-7a1的末端环，人类和其他高等真核生物中保守的KRKK基序增加了额外的结合界面，并通过静电相互作用增强了TruB1对pri-let-7a1的识别。这些发现揭示了TruB1-pri-let-7相互作用的结构基础，这可能有助于阐明TruB1在let-7生物发生中的精确作用。
