MicroRNAs are evolutionarily conserved small, noncoding RNAs that regulate diverse biological processes. Due to their essential regulatory roles, microRNA biogenesis is tightly regulated, where protein factors are often found to interact with specific primary and precursor microRNAs for regulation. Here, using NMR relaxation dispersion spectroscopy and mutagenesis, we reveal that the precursor of oncogenic microRNA-21 exists as a pH-dependent ensemble that spontaneously reshuffles the secondary structure of the entire apical stem-loop region, including the Dicer cleavage site. We show that the alternative excited conformation transiently sequesters the bulged adenine into a noncanonical protonated A⁺-G mismatch, conferring a substantial enhancement in Dicer processing over its ground conformational state. These results indicate that microRNA maturation efficiency may be encoded in the intrinsic dynamic ensemble of primary and precursor microRNAs, providing a potential means of regulating microRNA biogenesis in response to environmental and cellular stimuli.

MicroRNA是进化保守的小的非编码RNA，可调节多种生物过程。由于其必不可少的调节作用，microRNA的生物发生受到严格的调节，其中经常发现蛋白质因子与特定的初级和前体microRNA相互作用进行调节。在这里，使用核磁共振弛豫分散谱法和诱变，我们揭示致癌的microRNA-21的前体作为pH依赖的整体存在，自发地改组整个顶茎茎环区域的二级结构，包括切酶切酶位点。我们表明，替代的激发构象将螯合的腺嘌呤暂时隔离成非规范的质子化A ⁺-G不匹配，在Dicer处理过程中大大增强了其基本构象状态。这些结果表明，microRNA成熟效率可以在初级和前体microRNA的内在动态集合中编码，从而提供了一种潜在的手段，可以响应环境和细胞刺激来调节microRNA生物发生。