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

Nat Struct Mol Biol. 2009 Nov;16(11):1148-53. doi: 10.1038/nsmb.1673. Epub 2009 Oct 11.


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.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Argonaute Proteins
  • Eukaryotic Initiation Factor-2 / genetics
  • Eukaryotic Initiation Factor-2 / metabolism
  • Eukaryotic Initiation Factor-2 / ultrastructure
  • Humans
  • MicroRNAs / genetics
  • MicroRNAs / metabolism
  • Microscopy, Electron
  • Models, Biological
  • Protein Binding / genetics
  • RNA, Small Interfering / genetics
  • RNA, Small Interfering / metabolism
  • RNA-Binding Proteins / genetics
  • RNA-Binding Proteins / metabolism
  • RNA-Binding Proteins / ultrastructure
  • RNA-Induced Silencing Complex / chemistry*
  • RNA-Induced Silencing Complex / metabolism*
  • RNA-Induced Silencing Complex / ultrastructure
  • Ribonuclease III / genetics
  • Ribonuclease III / ultrastructure


  • AGO2 protein, human
  • Argonaute Proteins
  • Eukaryotic Initiation Factor-2
  • MicroRNAs
  • RNA, Small Interfering
  • RNA-Binding Proteins
  • RNA-Induced Silencing Complex
  • trans-activation responsive RNA-binding protein
  • Ribonuclease III