Small interfering RNAs (siRNA) are potent reagents for directed post-transcriptional gene silencing1 and a major new genetic tool for investigating mammalian cells. When synthetic siRNAs are used for gene silencing, the costs can be substantial because of variations in siRNA efficacies. An alternative to chemically synthesized siRNAs are siRNAs produced by bacteriophage T7 RNA polymerase. We found that siRNAs synthesized from the T7 RNA polymerase system can trigger a potent induction of interferon α and β in a variety of cell lines. Surprisingly, we also found very potent induction of interferon α and β by short single-stranded RNAs (ssRNAs) transcribed with T3, T7 and Sp6 RNA polymerases. Analyses of the potential mediators of this response revealed that the initiating 5′ triphosphate is required for interferon induction. We describe here an improved method for T7 siRNA synthesis that alleviates the interferon response while maintaining full efficacy of the siRNAs.
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This work was supported by a grant from the Arnold and Mabel Beckman Foundation and the National Institutes of Health (AI29329, AI42552 and HL074704 to J.J.R.). D. Kim is a Beckman Fellow.
The authors declare no competing financial interests.
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Kim, D., Longo, M., Han, Y. et al. Interferon induction by siRNAs and ssRNAs synthesized by phage polymerase. Nat Biotechnol 22, 321–325 (2004) doi:10.1038/nbt940
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