Figure 1.

Basic pathway for miRNA biogenesis. Pri-miRNA is transcribed from a miRNA gene by RNA polymerase II (Pol II). DROSHA and DiGeorge syndrome critical region gene 8 (DGCR8) then bind together to form a microprocessor complex, which cleaves pri-miRNA to pre-miRNA. Pre-miRNA is exported from the nucleus to the cytoplasm by exportin-5 (EXP-5), where DICER converts pre-miRNA to mature miRNA along with TAR RNA-binding protein (TRBP) or PACT (also known as PRKRA) and Argonaute protein (AGO). DICER, TRBP or PACT, and AGO mediate duplex separation and loading of the mature miRNA into the RISC complex (RNA-induced silencing complex), whereby the miRNA can regulate gene expression.