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. Author manuscript; available in PMC: 2010 Mar 1.
Published in final edited form as: Mol Reprod Dev. 2009 Mar;76(3):255–269. doi: 10.1002/mrd.20950

Figure 1.

Figure 1

Summary of miRNA processing machinery. In the nucleus miRNA are transcribed by RNA polymerase and are termed primary miRNAs (1°miRNAs). The dsRNA-specific ribonuclease RNASEN (Drosha) digests the 1°miRNAs in the nuclease to release hairpins, precursor miRNA (pre-miRNA) which are transported from the nucleus to the cytoplasm by exportins. Once in the cytoplasm, DICER cleaves the pre-miRNA approximately 19 bp from the Drosha cut site. The resulting double-stranded RNA has 1–4 nt 3′ overhangs at either end. Only one of the two strands is the mature miRNA. To control the translation of target mRNAs, the double-stranded RNA produced by DICER must strand separate, and the single-stranded mature miRNA must associate with the RISC. Post- transcriptional modifications such as splicing and editing play a part in miRNA processing.