Molecular Cell
Volume 44, Issue 3, 4 November 2011, Pages 502-508
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Short Article
Autoantigen La Promotes Efficient RNAi, Antiviral Response, and Transposon Silencing by Facilitating Multiple-Turnover RISC Catalysis

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Summary

The effector of RNA interference (RNAi) is the RNA-induced silencing complex (RISC). C3PO promotes the activation of RISC by degrading the Argonaute2 (Ago2)-nicked passenger strand of duplex siRNA. Active RISC is a multiple-turnover enzyme that uses the guide strand of siRNA to direct the Ago2-mediated sequence-specific cleavage of complementary mRNA. How this effector step of RNAi is regulated is currently unknown. Here, we used the human Ago2 minimal RISC system to purify Sjögren's syndrome antigen B (SSB)/autoantigen La as an activator of the RISC-mediated mRNA cleavage activity. Our reconstitution studies showed that La could promote multiple-turnover RISC catalysis by facilitating the release of cleaved mRNA from RISC. Moreover, we demonstrated that La was required for efficient RNAi, antiviral defense, and transposon silencing in vivo. Taken together, the findings of C3PO and La reveal a general concept that regulatory factors are required to remove Ago2-cleaved products to assemble or restore active RISC.

Highlights

► Autoantigen La is a novel activator of the RISC-mediated mRNA cleavage activity ► La promotes the multiple-turnover, but not single-turnover, RISC catalysis ► La promotes efficient RNAi, antiviral defense, and transposon silencing in vivo

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