In vitro binding of single-stranded RNA by human Dicer

While Dicer alone has been shown to form stable complexes with double-stranded RNAs and short interfering RNAs, its interactions with single-stranded RNAs (ssRNAs) have not been characterized. Here, we show that recombinant human Dicer alone can bind 21-nt ssRNAs in vitro, independent of their sequence and structure. We also demonstrate that Dicer binds ssRNAs having a 5′-phosphate with greater affinity versus those with a 5′-hydroxyl. In addition, 3′-biotinylated ssRNAs are bound by Dicer with lower affinity than 3′-hydroxyl ssRNAs. The stability of ssRNA–Dicer complexes was found to depend on divalent cations. Together, our results suggest a role for the PAZ domain of Dicer in binding ssRNAs and may indicate roles for Dicer in cellular function beyond those currently known.