Synthetic Dicer-Substrate siRNAs as Triggers of RNA Interference

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Abstract

The first synthetic oligonucleotides used to suppress gene expression in mammalian cells via RNA interference were 21-nucleotide (nt) RNA duplexes having symmetric 2-nt 3′-overhangs and were designed to mimic the natural products of Dicer processing of long RNA substrates. Synthetic RNA duplexes which are longer than 23-nt length are substrates for processing by Dicer and can show increased potency as artificial triggers of RNA interference, particularly at a low concentration. Longer duplexes, however, can have variable cleavage patterns following Dicer processing which can adversely affect potency. Optimized synthetic Dicer substrates are asymmetric duplexes having a 25-nt passenger strand and a 27-nt guide strand with a single 2-nt 3′-overhang on the guide strand and modified bases at the 3′-end of the passenger strand. This modified design results in predictable patterns of Dicer processing and shows improved activity. The development of this design strategy and use of Dicer-substrate RNAs to trigger gene suppression in a variety of systems will be reviewed in this chapter.