Figure 1.

MicroRNA biogenesis and RNA-induced gene silencing. Transcription of primary micro RNA (Pri-miRNA) from miRNA genes is followed by cleavage to precursor mRNA (Pre-miRNA) by the Drosha nuclear RNase III. The Pre-miRNA is then exported to the cytoplasm by exportin via nuclear pore. In the cytoplasm, Pre-miRNA is further processed by RNase activity of Dicer to the mature micro RNA duplex. The duplex loads onto Argonaut ribonucleases in the RISC complex and separates. One of the mature miRNA strands (red strand) mediates small interfering RNA silencing by degrading the target mRNA or interfering with translation. The outcome of RISC formation varies with the degree of complementarity of the seed sequence of miRNA and 3’ untranslated regions (UTR) of the target mRNA.