韩国基础科学研究所V. Narry Kim研究小组发现，DICER介导小RNA生产的序列决定因素。该研究于2023年2月22日在线发表于国际一流学术期刊《自然》。

据研究人员介绍，RNA沉默依赖于Dicer对双链RNA的特异性和高效处理，从而产生microRNA（miRNA）和小干扰RNA（siRNA）。然而，人们目前对Dicer特异性的了解仅限于其底物的二级结构：约22个碱基对的双链RNA，并带有2个核苷酸的3'突出和1个末端环。

研究人员发现的证据指向一个额外的序列依赖决定因素，其超出这些结构性质。为了系统地研究前体miRNA（pre-miRNA）的特征，研究人员人员使用pre-miRNA变体和人类DICER（也称为DICER1）进行了大规模的并行分析。这些分析揭示了一个高度保守的顺式作用元件，称为“GYM模体”(成对的G、成对的嘧啶和不匹配的C或A)，靠近切割位点。GYM模体促进特定位置的加工，并可以覆盖先前确定的pre-miRNA的5'和3'末端“尺子”样计数机制。一致地，将该模体整合到短发夹RNA或DICER底物siRNA中能够增强RNA干扰。

此外，研究人员发现DICER的C端双链RNA结合域（dsRBD）识别GYM模体。dsRBD的改变减少了加工过程，并以模体依赖的方式改变了切割位点，进而影响了细胞中的miRNA库。特别的是，癌症相关的R1855L在dsRBD中的替换强烈地损害了GYM模体的识别。这项研究揭示了后生动物Dicer识别底物的古老原理，并暗示了其在RNA治疗设计中的潜力。

附：英文原文

Title: Sequence determinant of small RNA production by DICER

Author: Lee, Young-Yoon, Kim, Haedong, Kim, V. Narry

Issue&Volume: 2023-02-22

Abstract: RNA silencing relies on specific and efficient processing of double-stranded RNA by Dicer, which yields microRNAs (miRNAs) and small interfering RNAs (siRNAs)1,2. However, our current knowledge of the specificity of Dicer is limited to the secondary structures of its substrates: a double-stranded RNA of approximately 22 base pairs with a 2-nucleotide 3′ overhang and a terminal loop3,4,5,6,7,8,9,10,11. Here we found evidence pointing to an additional sequence-dependent determinant beyond these structural properties. To systematically interrogate the features of precursor miRNAs (pre-miRNAs), we carried out massively parallel assays with pre-miRNA variants and human DICER (also known as DICER1). Our analyses revealed a deeply conserved cis-acting element, termed the ‘GYM motif’ (paired G, paired pyrimidine and mismatched C or A), near the cleavage site. The GYM motif promotes processing at a specific position and can override the previously identified ‘ruler’-like counting mechanisms from the 5′ and 3′ ends of pre-miRNA3,4,5,6. Consistently, integrating this motif into short hairpin RNA or Dicer-substrate siRNA potentiates RNA interference. Furthermore, we find that the C-terminal double-stranded RNA-binding domain (dsRBD) of DICER recognizes the GYM motif. Alterations in the dsRBD reduce processing and change cleavage sites in a motif-dependent fashion, affecting the miRNA repertoire in cells. In particular, the cancer-associated R1855L substitution in the dsRBD strongly impairs GYM motif recognition. This study uncovers an ancient principle of substrate recognition by metazoan Dicer and implicates its potential in the design of RNA therapeutics.

DOI: 10.1038/s41586-023-05722-4

Source: https://www.nature.com/articles/s41586-023-05722-4