In vitro binding of single‐stranded RNA by human Dicer

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Abstract
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.