FIGURE 1.

miRNA biogenesis. Transcription of miRNAs is mediated by RNA polymerase II. The pri-miRNAs are substrates for the rnase III, Drosha. The product of pre-miRNA cleavage by Drosha is exported to the cytoplasm by the nuclear transporter exportin 5. In the cytoplasm, DICER processes the pre-miRNA into a miRNA/miRNA* duplex. Final processing yields the mature miRNA duplex, the strand with lower thermodynamic stability is loaded into Argonaute (AGO); this is deemed the guide strand. The guide strand alongside AGO constitutes the minimal RNA-induced silencing complex (RISC). Once recruited the RISC complex onto the mRNA target, the inhibition of translation is carried out through cleavage, deadenylation, or blocking of the mRNA translation.