Figure 1.

Biogenesis of microRNAs. miRNA genes are transcribed in the nucleus, where they undergo processing by DGCR8/Pasha and the RNAse III family enzyme, Drosha. The pre-miRNA is then transported into the cytoplasm where it is processed by Dicer, and the cofactor TRBP to generate a ~22 nt miRNA:miRNA* duplex. After unwinding, the miRNA forms part of the RISC assembly and causes mRNA degradation or translational repression.