Fig. 1
From: MicroRNA let-7 and viral infections: focus on mechanisms of action
MicroRNA biogenesis. miRNAs are produced from miRNA genes, which are transcribed via RNA polymerase II/III to form primary miRNA termed pri-miRNA. Thereafter, pri-miRNA is cleaved by Drosha and DGCR8, and forms precursor microRNA (pre-miRNA), which is exported to the cytoplasm via Ran-GTP and exportin-5 to undergo maturation. miRNA duplex composed of mature miRNA is generated from cleaving the pre-miRNA, which is processed by Dicer and transactivation response element RNA-binding protein (TRBP). The single strand of mature miRNA, containing Ago-2 and GW182 proteins, binds to the complex, namely RISC. This complex modulates miRNA target gene expression by target miRNA cleavage and translation inhibition