Figure 4.

Biogenesis mechanism for miRNAs. The synthesis of miRNAs begins in the nucleus with the action of RNA polymerase II on a protein-coding. This forms a first species, called pri-miRNA. Through successive reactions of polyadenylation catalyzed by DGCR8 and Drosa, the precursor for the miRNAs species, called pre-miRNA, is obtained. pre-miRNA thus formed is transported into the cytoplasm through Exportin 5. In the cytoplasm, on the pre-miRNA acts the Dicer complex. Subsequently through the action of TRBP, AGO2 and Dicer is obtained the RNA induced silencing complex (RISC) and finnaly the mature miRNAs.