Figure 1.

miRs processing and mechanism of action. RNA polymerase II (Pol-II) transcribes the primary miR transcript (pri-miR) subsequently cleaved by Drosha-DGCR8 complex into pre-miR. The resulting pre-miR is exported from the nucleus to the cytoplasm by Exportin-5/Ran-GTP. RNase Dicer cleaves the pre-miR to its mature miR duplex that is loaded onto Argonaute (AGO1–4) proteins and forms the pre-effector RNA-induced silencing complex (pre-RISC). The guide strand is retained into the mature miR-induced RISC (mi-RISC) whereas the passenger strand (blue) is discarded. A full complementary base pairing induces the mRNA cleavage by AGO2 slicing activity, while a partial complementary induces translational repression, deadenylation, and decapping followed by mRNA target degradation.