Figure 1.

Biogenesis of miRNA. Transcription of miRNA by RNA polymerase II yields a long primary transcript (pri-miRNA) that contains a cap 5′ and poly-A tail. The complex DROSHA/DGCR8 cleaves pri-miRNA and gives rise to an miRNA precursor (pre-miRNA) that is exported to the cytoplasm and further processed by DICER endonuclease. An miRNA duplex associates with the RISC complex and retains the mature strand of miRNA. This complex directs imperfect binding to 3′-UTR region of target mRNA, leading to a reduction in protein levels via translation blockage and mRNA deadenylation and decay.