Figure 1

Biological functions of miRNA. The first step is the nuclear cleavage of the pri-miRNA, with a ~60-70 nt stem loop intermediate liberated, known as the miRNA precursor, or the pre-miRNA. Then this pre-miRNA is actively transported from the nucleus to the cytoplasm by Ran-GTP and export receptor. One end of the mature miRNA was cut by Drosha in nuclear and the other end is processed in the cytoplasm by the enzyme Dicer. Either of the strands becomes stably associated with RNA-induced silenced complex (RISC), which can be called miRISC complex. The miRISC complex inhibits the target genes by (A) repressing initiation at the cap recognition, (B) inducing deadenylation of mRNA and thereby inhibiting circularization of mRNA, (C) inducing ribosomes to drop off prematurely thus repressing the translation initiation and (D) promoting mRNA degradation.