(A) let-7 production was monitored using 5′ ³²P-radiolabeled pre-let-7 (100 nM) with or without ATP for Dicer-2 alone (8 nM), Dicer-2/R2D2 (8 nM), Dicer-2 + Loqs-PD (8 nM + 8 nM) or Dicer-2/R2D2 + Loqs-PD (8 nM + 8 nM). (B) Processing of internally ³²P-radiolabeled long dsRNA or 5′ ³²P-radiolabeled pre-let-7 (100 nM) by Dicer-2 (8 nM). CK, creatine kinase; CP, creatine phosphate. (C) Initial velocities for the processing of 100 nM pre-let-7 or long dsRNA (106 bp blunt ended or 104 bp with 2 nt, 3′ overhanging ends) by 8 nM Dicer-2 or Dicer-2/R2D2 in the presence of increasing concentrations of potassium phosphate. Total potassium in the reaction was kept constant. (D) Initial velocities for Dicer-2 processing pre-let-7, 106 bp blunt ended dsRNA or 104 bp dsRNA with 2 nt, 3′ overhanging ends in the presence of 25 mM potassium phosphate, acetate, chloride, or glutamate. (E) Processing of internally ³²P-radiolabeled long dsRNA or 5′ ³²P-radiolabeled pre-let-7 substrate (100 nM) by wild-type or G31R mutant Dicer-2 (8 nM) with or without ATP or with ATPγS (1 mM). Values are mean ± standard deviation for three independent experiments.

(A) Site-specifically ³²P-radiolabeled 120 bp dsRNAs were used to measure the rate of production of the first, second and fourth siRNAs from the all-RNA end of the substrate; the 32 end of the sense strand contained two deoxynucleotides (red) to block entry of Dicer-2 from the other end (Figure S4A). Production of siRNA was monitored in the presence or absence of ATP using 100 nM dsRNA and 5.4 nM Dicer-2. Values correspond to the mean ± standard deviation from three independent experiments. The data were fit to a single exponential function. In (A) and (B), pink denotes the position of the ³²P-radiolabel. (B) The rate of production of the initial siRNA was measured as in (A), but using a site-specifically ³²P-radiolabeled dsRNA with either a blunt (black) or a 2 nt 3′ overhanging (red) end in the presence or absence of ATP. (C) The rate of production of the initial siRNA was monitored using 100 nM Dicer-2 and 10 nM dsRNA bearing either a blunt (left) or a 2 nt 3′ overhanging (right) end in the presence or absence of ATP or ATPγS. (D) The rate of production of the initial siRNA from a 120 bp blunt ended dsRNA (10 nM) was measured using 100 nM mutant Dicer-2^G31R. (E) The rate of production of the first and fourth siRNAs from a 120 bp blunt ended dsRNA (100 nM) was measured using 100 nM Dicer-2^G31R. Values are mean ± standard deviation for three independent experiments.

A model for Drosophila Dicer-2

Synthetic, 5′ monophosphorylated pre-let-7 (1.0 µM) was incubated with Dicer-1 (6.0 nM) or Dicer-2 (16.2 nM) for 1 h. Products were resolved by electrophoresis. let-7 and let-7* were detected by Northern hybridization.

(A) Dicer-2 (10.8 nM) was incubated with 2.5 µM α-³²P ATP and 150 nM 515 bp dsRNA, and ATP hydrolysis monitored by thin-layer chromatography. (B) siRNA production by Dicer-2 (5.4 nM) from a 515 bp dsRNA (25 nM) was monitored with or without ATP or ATPγS (1 mM). (C) ATP hydrolysis by Dicer-2 (5.4 nM) was monitored for 120 nt long nucleic acid substrates (20 nM): dsRNA, single-stranded RNA, single-stranded DNA, RNA/DNA heteroduplex or double-stranded DNA in the presence of ATP (1 mM). (D) ATP hydrolysis by Dicer-2 (5.4 nM) in the presence of ATP (1 mM) was measured for 20 nM dsRNA bearing a 5′ monophosphate and a 2 nt 3′ overhang or blunt ends; the blunt ended dsRNA bearing either 5′ monophosphate or 5′ hydroxy termini. (E) ATP hydrolysis by mutant Dicer-2^D1217,1614N (3.3 nM) , Dicer-2^G31R (2 nM) and wild-type Dicer-2 (2 nM) was measured in the absence or presence of 20 nM dsRNA bearing 5′ monophosphate, blunt ends. (F) Left panel, initial rates for the conversion of substrate into siRNA by Dicer-2 (2.7 nM) for an internally ³²P-radiolabeled 515 bp dsRNA (150 nM) were measured at increasing concentrations of ATP. Right panel, initial rates for the hydrolysis of ATP to ADP by Dicer-2 in the presence of 150 nM, 515 bp dsRNA were measured for increasing ATP concentrations. The data were fit to the Michaelis-Menten equation. Table 2 reports the Michaelis-Menten parameters. (G) ATP consumption by Dicer-2 was measured in the presence of ATP (350 µM) and dsRNA substrates with blunt, 5′ triphosphorylated termini for six different lengths: 40 bp (420 nM), 60 bp (280 nM), 106 bp (158 nM), 208 bp (80.5 nM), 345 bp (49 nM), 558 bp (30 nM). Substrate concentrations were selected to ensure an equal number of base pairs in each reaction. Values are mean ± standard deviation for three independent experiments.

(A) Design of the experiment. The reaction contained 54 fmol Dicer-2 and 200 fmol dsRNA, corresponding to 5.4 nM enzyme and 20 nM dsRNA before dilution. (B) The rate of production of the fourth siRNA was measured for six different combinations of pre-incubation (no pre-incubation, without ATP, and with ATP) and dilution (without and with ATP). Values are mean ± standard deviation for three independent experiments.