Fig. 1.

Target mRNA degradation by RNAi gene silencing. Dicer initiates RNAi by cleaving dsRNAs into ~22 bp small interfering RNAs (siRNAs). During RISC assembly, Ago2 directly binds to the siRNA and cleaves sense siRNAs (blue strands) and only the anti-sense siRNAs (red strands) remain associated with the RISC complex. After assembly of RISC, the antisense strand directs RISC to target mRNAs. The RISC cut the target mRNAs at 11 to 12 bp downstream of the 5' end of the antisense strand covering the target mRNA.