Figure 1. .

miRNA biogenesis. The generation of miRNAs involves nuclear and cytoplasmic processing steps. In the nucleus, pri-miRNAs, transcribed by RNA polymerase from DNA, are processed by Drosha into pre-miRNAs that are then transported to cytoplasm via exportin 5. Once in the cytoplasm, these pre-miRNAs are recognized and cleaved by Dicer into 20 to 22 bp duplexes that enter RISC. In RISC, the passenger strand is cleaved while the guide strand directs RISC machinery to target mRNAs resulting in mRNA degradation or inhibition of protein translation.