Synthetic small interfering RNAs (siRNAs) are an indispensable tool to investigate gene function in eukaryotic cells1,2 and may be used for therapeutic purposes to knock down genes implicated in disease3. Thus far, most synthetic siRNAs have been produced by chemical synthesis. Here we present a method to produce highly potent siRNAs in Escherichia coli. This method relies on ectopic expression of p19, an siRNA-binding protein found in a plant RNA virus4,5. When expressed in E. coli, p19 stabilizes an ∼21-nt siRNA-like species produced by bacterial RNase III. When mammalian cells are transfected by them, siRNAs that were generated in bacteria expressing p19 and a hairpin RNA encoding 200 or more nucleotides of a target gene reproducibly knock down target gene expression by ∼90% without immunogenicity or off-target effects. Because bacterially produced siRNAs contain multiple sequences against a target gene, they may be especially useful for suppressing polymorphic cellular or viral genes.
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The authors thank J. Carrington (Donald Danforth Plant Science Center) for the p19 clone, C. Zhang and G. Ruvkun (Massachusetts General Hospital) for L4440 plasmid and HT115(DE3) strain, S. Kushner (University of Georgia) for SK7622 strain, D. Higgins (Harvard Medical School) for pLIV-1 plasmid, and S. Ranjbar (Boston Children's Hospital) for HIV strains and cell lines. We thank L.M. Mazzola, J.M. Bybee and D.B. Munafo from New England Biolabs for assistance with RNA deep sequencing and Z. Ansara for technical help. We thank A. Hochschild (Harvard Medical School) for suggestions and critical reading of the manuscript and Lieberman Lab members for technical assistance, helpful discussions and comments on the manuscript. This work was supported by National Institutes of Health grant AI087431 (J.L.) and a GSK-IDI Alliance fellowship (L.H.).
J.J. and L.M. are employees of New England Biolabs, a company that sells deep sequencing kits, p19 and other proteins for RNA and DNA research.
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Huang, L., Jin, J., Deighan, P. et al. Efficient and specific gene knockdown by small interfering RNAs produced in bacteria. Nat Biotechnol 31, 350–356 (2013). https://doi.org/10.1038/nbt.2537
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