Double-stranded RNA (dsRNA) endoribonuclease playing a central role in short dsRNA-mediated post-transcriptional gene silencing. Cleaves naturally occurring long dsRNAs and short hairpin pre-microRNAs (miRNA) into fragments of twenty-one to twenty-three nucleotides with 3' overhang of two nucleotides, producing respectively short interfering RNAs (siRNA) and mature microRNAs. SiRNAs and miRNAs serve as guide to direct the RNA-induced silencing complex (RISC) to complementary RNAs to degrade them or prevent their translation. Gene silencing mediated by siRNAs, also called RNA interference, controls the elimination of transcripts from mobile and repetitive DNA elements of the genome but also the degradation of exogenous RNA of viral origin for instance. The miRNA pathway on the other side is a mean to specifically regulate the expression of target genes (By similarity). Endonucleolytic cleavage to 5'-phosphomonoester. Binds 2 magnesium or manganese ions per subunit. Component of the RISC loading complex (RLC), or micro-RNA (miRNA) loading complex (miRLC), which is composed of dicer1, ago2 and tarbp2; dicer1 and tarbp2 are required to process precursor miRNAs (pre-miRNAs) to mature miRNAs and then load them onto ago2. Note that the trimeric RLC/miRLC is also referred to as RISC (By similarity). Belongs to the helicase family. Dicer subfamily.