Short interfering RNAs (siRNAs) and microRNAs (miRNAs) are both processed from longer, double-stranded RNA (dsRNA) presursors by a member of the Dicer (Dcr) family of proteins. siRNAs generally arise from perfectly base-paired dsRNAs, whereas miRNAs are excised from 60-70 nt pre-miRNA hairpins containing multiple bulges and mismatches within the duplexed...