Figure 1.

Biogenesis and function of miRNAs. miRNAs are transcribed from specific genes by RNA polymerase II, followed by their cleavage with enzymes Drosha and DGCR8 in the nucleus. The cleaved miRNA is then transported to the cytoplasm by Expotin 5 and Ran GTP where it is further acted upon by the enzyme Dicer to form the mature miRNA duplex. Each strand of the duplex then mediates silencing by either complete base-pairing or incomplete base-pairing with the target mRNA. This reaction is catalyzed by a couple of enzymes which together form the RNA-induced silencing complex (RISC).