Figure 1

The biogenesis of miRNAs. RNA polymerase II transcribes miRNA gene, generating a long primary transcript (pri miRNA). Drosha-mediated cleavage of pri-miRNA leads to the formation of a hairpin molecule, the pre-microRNA that is exported to the cytoplasm by the complex exportin-5/RAN-GTP. In the cytoplasm, Dicer cleaves the pre-miRNA and produces a ~22-nt RNA duplex. The functional strand of the duplex is incorporated into a multiple-protein nuclease complex, the RNA-induced silencing complex (RISC), which regulates protein expression.