In animals, the majority of microRNAs regulate gene expression through the RNA interference (RNAi) machinery without inducing small-interfering RNA (siRNA)-directed mRNA cleavage1. Thus, the mechanisms by which microRNAs repress their targets have remained elusive. Recently, Argonaute proteins, which are key RNAi effector components, and their target mRNAs were shown to localize to cytoplasmic foci known as P-bodies or GW-bodies2,3. Here, we show that the Argonaute proteins physically interact with a key P-/GW-body subunit, GW182. Silencing of GW182 delocalizes resident P-/GW-body proteins and impairs the silencing of microRNA reporters. Moreover, mutations that prevent Argonaute proteins from localizing in P-/GW-bodies prevent translational repression of mRNAs even when Argonaute is tethered to its target in a siRNA-independent fashion. Thus, our results support a functional link between cytoplasmic P-bodies and the ability of a microRNA to repress expression of a target mRNA.
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We thank S. Hearn from the Cold Spring Harbor Laboratory microscopy shared resource for assistance, and N. Gehring (European Molecular Biology Laboratory, Heidelberg), W. Filipowicz (Friedrich Miescher Institute), M. Kiledjian (Rutgers University), J. Lykke-Andersen (University of Colorado), M. Fritzler (University of Calgary) and E. Chan (University of Florida) for reagents. F.V.R. is a fellow of the Jane Coffin Childs Foundation, and J.L. is supported as a Special Fellow of the Leukemia and Lymphoma Society. This work was supported by grants from the National Institutes of Health (G.J.H and R.P). G.J.H. and R.P. are Investigators of the Howard Hughes Medical Institute.
The authors declare no competing financial interests.
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