Partin Alexander C, Zhang Kaiming, Jeong Byung-Cheon, Herrell Emily, Li Shanshan, Chiu Wah, Nam Yunsun
Laboratory of RNA Biology, Cecil H. and Ida Green Center for Reproductive Biology Sciences, University of Texas Southwestern Medical Center, Dallas, TX 75390, USA; Departments of Biophysics and Obstetrics and Gynecology, University of Texas Southwestern Medical Center, Dallas, TX 75390, USA.
Department of Bioengineering and James H. Clark Center, Stanford University, Stanford, CA 94305, USA.
Mol Cell. 2020 May 7;78(3):411-422.e4. doi: 10.1016/j.molcel.2020.02.016. Epub 2020 Mar 27.
Metazoan microRNAs require specific maturation steps initiated by Microprocessor, comprising Drosha and DGCR8. Lack of structural information for the assembled complex has hindered an understanding of how Microprocessor recognizes primary microRNA transcripts (pri-miRNAs). Here we present a cryoelectron microscopy structure of human Microprocessor with a pri-miRNA docked in the active site, poised for cleavage. The basal junction is recognized by a four-way intramolecular junction in Drosha, triggered by the Belt and Wedge regions that clamp over the ssRNA. The belt is important for efficiency and accuracy of pri-miRNA processing. Two dsRBDs form a molecular ruler to measure the stem length between the two dsRNA-ssRNA junctions. The specific organization of the dsRBDs near the apical junction is independent of Drosha core domains, as observed in a second structure in the partially docked state. Collectively, we derive a molecular model to explain how Microprocessor recognizes a pri-miRNA and accurately identifies the cleavage site.
后生动物的微小RNA需要由微处理器启动特定的成熟步骤，微处理器由Drosha和DGCR8组成。缺乏组装复合物的结构信息阻碍了人们对微处理器如何识别初级微小RNA转录本（pri-miRNA）的理解。在此，我们展示了人类微处理器与对接在活性位点、准备进行切割的pri-miRNA的冷冻电镜结构。基部连接由Drosha中的一个四向分子内连接识别，该连接由夹在单链RNA上的带和楔区域触发。带对于pri-miRNA加工的效率和准确性很重要。两个双链RNA结合结构域（dsRBD）形成一个分子尺来测量两个双链RNA-单链RNA连接之间的茎长度。如在部分对接状态下的第二个结构中所观察到的，顶端连接附近dsRBD的特定组织独立于Drosha核心结构域。我们共同推导了一个分子模型来解释微处理器如何识别pri-miRNA并准确识别切割位点。
