Fig. 1

The majority of miRNA genes are transcribed by the RNA polymerase II (Pol II) as primary miRNAs (pri-miRNAs) which are processed to precursor miRNAs (pre-miRNAs) via the Drosha-DGR8 complex. Pre-mRNAs are exported to the cytoplasm by Exportin-5-Ran-GTP (Xpo-5-RanGTP) where Dicer1 cleaves the hairpin loop and Tar RNA-binding protein 2 (TARBP2) facilitates the RNA duplex loading onto Argonaute protein AGO2. AGO2 and the mature strand enter a protein effector complex formed by the RNA-induced silencing complex (miRISC). The miRNA guides the RISC to messenger RNA targets causing either mRNA cleavage (perfect complementarity) or translational repression (imperfect complementarity)