Figure 2.

MicroRNA biogenesis. The protein Drosha, a member of the RNase III family, processes primary transcripts as part of the Microprocessor complex. The hairpins are exported to the cytoplasm via a complex of Exportin-5 and GTP-bound Ran (RanGTP). Once in the cytoplasm, the microRNA precursor is further processed by the RNase III Dicer in a complex with TAR RNA binding protein (TRBP) to give a mature double-stranded microRNA. A single-stranded microRNA is then handed over to the RISC. Ectopically expressed shRNAs can compete for various components of this pathway, and can thereby affect the levels of endogenous microRNAs that enter RISC.