4.7 Article

A human, ATP-independent, RISC assembly machine fueled by pre-miRNA

Journal

GENES & DEVELOPMENT
Volume 19, Issue 24, Pages 2979-2990

Publisher

COLD SPRING HARBOR LAB PRESS, PUBLICATIONS DEPT
DOI: 10.1101/gad.1384005

Keywords

miRNA; miRNP; Dicer; Argonaute; siRNA; RNAi

Funding

  1. NCI NIH HHS [P30 CA016520, P30-CA016520] Funding Source: Medline
  2. NICHD NIH HHS [P30 HD026979, P30-HD026979] Funding Source: Medline
  3. NIGMS NIH HHS [R01-GM0720777] Funding Source: Medline

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RNA interference (RNAi) is mediated by RNA-induced silencing complexes (RISCs), which are guided by microRNAs (miRNAs) or short interfering RNAs (siRNAs) to cognate RNA targets. In humans, the catalytic engine of RISC is a ribonucleoprotein formed by the Argonaute2 (Ago2) protein and either miRNA (miRNP) or siRNA (siRNP). The Dicer nuclease produces mature miRNAs and siRNAs from pre-miRNAs and double-stranded RNA (dsRNA), respectively, and associates with Ago2. Here, we studied the assembly of human RISC by presenting pre-miRNA to immunopurified complexes that contain Ago2, Dicer, and TRBP. Mature miRNAs were produced in an ATP-independent manner and guided specific cleavage of cognate RNA targets in a pattern that is typical of RISC. This de novo formed RISC activity dissociated from Dicer. The asymmetry of the RISC loading process was fully recapitulated in this system, which, however, could not efficiently assemble RISC from siRNA duplexes. Our findings demonstrate that, in humans, a miRNA loading complex (miRLC) is formed by Ago2 and Dicer prior to their encounter with pre-miRNA. We suggest that the miRLC couples the processing of the pre-miRNA substrate to the unwinding of the product and that after loading of the mature miRNA to Ago2, the miRLC disassembles and the miRNP is released.

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