Figure 1

MicroRNA biogenesis pathways and their regulation: a schematic representation depicting the miRNA biogenesis pathway. The primary miRNA transcript (pri-miRNA) by RNA polymerase II or III and cleavage of the pri-miRNA by the microprocessor complex Drosha-DGC8 in the nucleus. The resulting precursor hairpin, the pre-miRNA, is exported from the nucleus by exportin-5-Ran-GTP. In the cytoplasm, the RNase Dicer form complex with the double-stranded RNA-binding protein TRBP cleaves the pre-miRNA hairpin to its mature length. The functional strand of the mature miRNA is loaded together with Argonaute (Ago2) proteins into the RNA-induced silencing complex (RISC), where it targets mRNAs through mRNA cleavage, deadenylation or translational repression, where as passenger strand (3′---------5′) is degraded.