Figure 1.

Schematic representation of biogenesis and posttranscriptional suppression of microRNAs: In the nucleus, the nascent primary microRNA (pri‐miRNA) transcripts are processed into ~70 nucleotide precursor miRNAs (pre‐miRNAs) by Drosha. Pre‐miRNAs are transported to the cytoplasm by exportin‐5 and the enzyme dicer process pre‐miRNA into miRNA: miRNA* duplexes. Then, one strand of short double‐stranded RNA is degraded (passenger strand); the other strand (miRNA) is then associated with a number of proteins collectively known as the RNA‐induced silencing complex (RISC), forming miRNA–protein complex. RISC acts on its target to downregulate gene expression by different posttranscriptional mechanisms: mRNA cleavage or translational repression or destabilization of the mRNA through shortening of its poly(A) tail.