Fig. (1).

Biogenesis of microRNA. MicroRNA (miRNA) genes are typically transcribed into primary miRNA (pri-miRNA) transcripts that undergo processing by Drosha-containing complexes in animals. The unified hairpin precursor miRNAs (pre-miRNAs) are transported to the cytoplasm by exportin 5 (XPO5). The Dicer complex removes the loop region from pre-miRNAs, and one strand of the resulting duplex is bound by Argonaute to form a miRNA-induced silencing complex (miRISC). After multiple processing, mature miRNAs target complementary transcripts and downregulate gene expression by mRNA degradation or translational repression.