Figure 1.

Biogenesis of native intronic microRNA (miRNA). Intronic miRNA is co-transcribed within a precursor messenger RNA (pre-mRNA) by eukaryotic type-II RNA polymerases (Pol-II) and cleaved out of the pre-mRNA by RNA splicing. While the exons are ligated to form a mature messenger RNA (mRNA) for protein synthesis, the spliced intron(s) with a high secondary structure (ie, hairpin and/or stem-loop) is further processed into mature miRNA capable of triggering post-transcriptional gene silencing (PTGS) effects, such as RNA interference (RNAi).