Fig. 1.
miRNA biogenesis and RISC assembly in human cells. miRNA are initially transcribed as pri-miRNA, processed by the complex of Drosha and DGCR8 to pre-miRNA, exported to the cytosol by exportin-5, and cleaved to a mature miRNA guide strand and passenger strand (miRNA*) by the complex of Dicer and TRBP. For RISC assembly, the mature guide strand (red strand in illustration) is loaded onto an AGO protein along with other assembly proteins not illustrated. The passenger strand is degraded while the guide strand interacts with specific target sites in the 3′-UTR of transcripts. Near perfect complementarity between the target transcript and the seed sequence of the miRNA is required to effectuate an inhibitory response.