siRNA Repositioning for Guide Strand Selection by Human Dicer Complexes

• Published in: Molecular cell Vol. 43; no. 1; pp. 110 - 121
• Main Authors: Noland, Cameron L., Ma, Enbo, Doudna, Jennifer A.
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 08.07.2011
• Subjects: Binding Sites; biogenesis; double-stranded RNA; Humans; Models, Genetic; Ribonuclease III - physiology; ribonucleases; RNA, Small Interfering - chemistry; RNA, Small Interfering - metabolism; RNA-Induced Silencing Complex - chemistry; RNA-Induced Silencing Complex - metabolism; small interfering RNA; Thermodynamics
• ISSN: 1097-2765; 1097-4164
• DOI: 10.1016/j.molcel.2011.05.028

The human ribonuclease Dicer and its double-stranded RNA (dsRNA)-binding protein (dsRBP) partners TRBP and PACT play important roles in the biogenesis of regulatory RNAs. Following dicing, one dsRNA product strand is preferentially assembled into an RNA-induced silencing complex (RISC). The mechanism of strand selection in humans and the possible role of Dicer in this process remain unclear. Here we demonstrate that dsRNAs undergo significant repositioning within Dicer complexes following dicing. This repositioning enables directional binding of RNA duplexes, thereby biasing their orientation for guide strand selection according to the thermodynamic properties of the helix. Our findings indicate that Dicer is itself capable of sensing siRNA thermodynamic asymmetry regardless of the dsRBP to which it is bound. These results support a model in which Dicer employs two distinct RNA-binding sites—one for dsRNA processing and the other for sensing of siRNA thermodynamic asymmetry—during RISC loading in humans. ► Dicer/TRBP repositions products along Dicer's helicase domain ► Dicer/TRBP releases nascent product RNAs prior to repositioning ► dsRBPs position siRNAs for sensing of thermodynamic asymmetry by Dicer