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J Biol Chem. 2007 Nov 9;282(45):32773-9. Epub 2007 Aug 27.

P68 RNA helicase unwinds the human let-7 microRNA precursor duplex and is required for let-7-directed silencing of gene expression.

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Department of Molecular, Microbial, and Structural Biology, University of Connecticut Health Center, 236 Farmington Avenue, Farmington, CT 06030, USA.


MicroRNAs are short, single-stranded RNAs that arise from a transient precursor duplex. We have identified a novel activity in HeLa cell extracts that can unwind the let-7 microRNA duplex. Using partially purified material, we have shown that microRNA helicase activity requires ATP and has a native molecular mass of approximately 68 kDa. Affinity purification of the unwinding activity revealed co-purification of P68 RNA helicase. Importantly, recombinant P68 RNA helicase was sufficient to unwind the let-7 duplex. Moreover, like its native homolog, P68 RNA helicase did not unwind an analogous small interfering RNA duplex. We further showed that knockdown of P68 inhibited let-7 microRNA function. From our data, we conclude that P68 RNA helicase is an essential component of the let-7 microRNA pathway, and in conjunction with other factors, it may play a role in the loading of let-7 microRNA into the silencing complex.

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