 Endogenous dsRNA initiates RNAi by activating the ribonuclease protein Dicer , which binds and cleaves double @-@ stranded RNAs ( dsRNAs ) to produce double @-@ stranded fragments of 20 – 25 base pairs with a 2 @-@ nucleotide overhang at the 3 ' end . Bioinformatics studies on the genomes of multiple organisms suggest this length maximizes target @-@ gene specificity and minimizes non @-@ specific effects . These short double @-@ stranded fragments are called small interfering RNAs ( siRNAs ) . These siRNAs are then separated into single strands and integrated into an active RISC complex . After integration into the RISC , siRNAs base @-@ pair to their target mRNA and cleave it , thereby preventing it from being used as a translation template . 
