Figure 1.

The mechanistic actions of siRNA and miRNA derived from genome. siRNA: Dicer processes dsRNA (either transcribed or artificially introduced) into siRNA, which is then loaded into the RISC. AGO2, a component of RISC, cleaves the passenger strand of siRNA. The guide strand guides the active RISC to the target mRNA and binds to the target mRNA completely, leading to the cleavage of mRNA. miRNA: miRNA gene is transcribed by RNA polymerase II in the nucleus to pri-miRNA, which is then cleaved by Drosha to form pre-miRNA. The pre-miRNA is transported by Exportin-5 to the cytoplasm and then processed by Dicer to miRNA, which is loaded into the RISC. The passenger strand is removed and the remaining strand guides the RISC to the target mRNA through partially complementary binding to the miRNA response elements within 3'UTR, leading to translational repression, degradation or cleavage of the target mRNA.