Figure 1.

Biogenesis of miRNAs and mode of action. pri-miRNAs are transcribed from the intra- and inter-genetic regions of the genome by RNA Pol II, followed by processing by the RNase III enzyme Drosha into premiRNAs. After nuclear export, they are cleaved by the RNase III enzyme Dicer into mature miRNAs consisting of ∼23 nucleotides. Finally, a single-stranded miRNA is loaded onto the miRISC, where the seed sequence is located at positions 2–7 from the 5′ end of the miRNA binding to the target mRNA thus inhibiting gene transcription.