Figure 2.

microRNA (miRNA) biogenesis. Biogenesis of miRNA begins with the generation of the pri-miRNA transcript. The microprocessor complex, Drosha/DGCR8, produces the pre-miRNA by cleaving pri-miRNA. The pre-miRNA is exported to the cytoplasm in an Exportin 5-dependent manner and undergoes cytoplasmic processing to produce the mature miRNA duplex (miRNA:miRNA*, passenger strand indicated by an asterisk) by the Dicer/ transactivation response element RNA-binding protein (TRBP) complex. Either the miRNA or miRNA* strands of the mature miRNA duplex is assembled into the effector complex RNA-induced silencing complex (RISC). The passenger miRNA strand is degraded and mature miRNA functions as a guide by base-pairing with the target mRNA to negatively regulate its expression. The direct gene silencing induced by mature miRNA via mRNA cleavage or translation repression is based on the level of complementarity between the miRNA and the mRNA target.