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Mechanism of siRNA production by a plant Dicer-RNA complex in dicing-competent conformation
Science  (IF47.728),  Pub Date : 2021-10-14, DOI: 10.1126/science.abl4546
Qian Wang, Yan Xue, Laixing Zhang, Zhenhui Zhong, Suhua Feng, Changshi Wang, Lifan Xiao, Zhenlin Yang, C. Jake Harris, Zhe Wu, Jixian Zhai, Maojun Yang, Sisi Li, Steven E. Jacobsen, Jiamu Du

In eukaryotes, small RNAs (sRNAs) play critical roles in multiple biological processes. Dicer endonucleases are central to sRNA biogenesis. In plants, DICER-LIKE PROTEIN 3 (DCL3) produces 24-nt small interfering RNAs (siRNAs) that determine the specificity of the RNA-directed DNA methylation (RdDM) pathway. Here, we determined structure of a DCL3-pre-siRNA complex in an active dicing-competent state. The 5′-phosphorylated-A1 of the guide strand and the 1-nt 3′-overhang of the complementary strand are specifically recognized by a positively charged pocket and an aromatic cap, respectively. The 24-nt siRNA length dependence relies on the separation between the 5′-phosphorylated-end of the guide RNA and dual cleavage sites formed by the paired RNaseIII domains. These structural studies, complemented by functional data, reveal insights into the dicing principle for Dicers in general.