Structural insights into RNA processing by the human RISC-loading complex.

Research paper by Hong-Wei HW Wang, Cameron C Noland, Bunpote B Siridechadilok, David W DW Taylor, Enbo E Ma, Karin K Felderer, Jennifer A JA Doudna, Eva E Nogales

Indexed on: 13 Oct '09Published on: 13 Oct '09Published in: Nature Structural and Molecular Biology


Targeted gene silencing by RNA interference (RNAi) requires loading of a short guide RNA (small interfering RNA (siRNA) or microRNA (miRNA)) onto an Argonaute protein to form the functional center of an RNA-induced silencing complex (RISC). In humans, Argonaute2 (AGO2) assembles with the guide RNA-generating enzyme Dicer and the RNA-binding protein TRBP to form a RISC-loading complex (RLC), which is necessary for efficient transfer of nascent siRNAs and miRNAs from Dicer to AGO2. Here, using single-particle EM analysis, we show that human Dicer has an L-shaped structure. The RLC Dicer's N-terminal DExH/D domain, located in a short 'base branch', interacts with TRBP, whereas its C-terminal catalytic domains in the main body are proximal to AGO2. A model generated by docking the available atomic structures of Dicer and Argonaute homologs into the RLC reconstruction suggests a mechanism for siRNA transfer from Dicer to AGO2.