Quick-Cleveland Jen, Jacob Jose P, Weitz Sara H, Shoffner Grant, Senturia Rachel, Guo Feng
Department of Biological Chemistry, David Geffen School of Medicine, University of California, Los Angeles, Los Angeles, CA 90095, USA.
Molecular, Cell and Integrative Physiology, University of California, Los Angeles, Los Angeles, CA 90095, USA.
Cell Rep. 2014 Jun 26;7(6):1994-2005. doi: 10.1016/j.celrep.2014.05.013. Epub 2014 Jun 6.
Canonical primary microRNA transcripts (pri-miRNAs) are characterized by a ∼30 bp hairpin flanked by single-stranded regions. These pri-miRNAs are recognized and cleaved by the Microprocessor complex consisting of the Drosha nuclease and its obligate RNA-binding partner DGCR8. It is not well understood how the Microprocessor specifically recognizes pri-miRNA substrates. Here, we show that in addition to the well-known double-stranded RNA-binding domains, DGCR8 uses a dimeric heme-binding domain to directly contact pri-miRNAs. This RNA-binding heme domain (Rhed) directs two DGCR8 dimers to bind each pri-miRNA hairpin. The two Rhed-binding sites are located at both ends of the hairpin. The Rhed and its RNA-binding surface are important for pri-miRNA processing activity. Additionally, the heme cofactor is required for formation of processing-competent DGCR8-pri-miRNA complexes. Our study reveals a unique protein-RNA interaction central to pri-miRNA recognition. We propose a unifying model in which two DGCR8 dimers clamp a pri-miRNA hairpin using their Rheds.
典型的初级微小RNA转录本（pri-miRNAs）的特征是具有一个约30个碱基对的发夹结构，两侧为单链区域。这些pri-miRNAs被由Drosha核酸酶及其必需的RNA结合伴侣DGCR8组成的微处理器复合物识别并切割。目前尚不清楚微处理器如何特异性识别pri-miRNA底物。在这里，我们表明，除了众所周知的双链RNA结合结构域外，DGCR8还使用一个二聚体血红素结合结构域直接接触pri-miRNAs。这个RNA结合血红素结构域（Rhed）引导两个DGCR8二聚体结合每个pri-miRNA发夹。两个Rhed结合位点位于发夹的两端。Rhed及其RNA结合表面对pri-miRNA加工活性很重要。此外，血红素辅因子是形成具有加工能力的DGCR8-pri-miRNA复合物所必需的。我们的研究揭示了pri-miRNA识别过程中一个独特的蛋白质-RNA相互作用核心。我们提出了一个统一模型，其中两个DGCR8二聚体使用它们的Rhed夹住一个pri-miRNA发夹。
