FIGURE 10-29 Processing of miRNA. This diagram shows transcription and processing of the miR-1-1 miRNA. The primary miRNA transcript (pri-miRNA) is transcribed by RNA polymerase II. The nuclear double-stranded RNA–specific endoribonuclease Drosha, with its partner, double-stranded RNA–binding protein DGCR8 (Pasha in Drosophila), makes the initial cleavages in the pri-miRNA, generating a ~70-nucleotide pre-miRNA that is exported to the cytoplasm by nuclear transporter exportin 5. The pre-miRNA is further processed in the cytoplasm by Dicer, in conjunction with the double-stranded RNA–binding protein TRBP (Loquacious in Drosophila), into a double-stranded miRNA with two-base single-stranded 3′ ends. Finally, one of the two strands is incorporated into a RISC complex, where it is bound by an Argonaute protein. See P. D. Zamore and B. Haley, 2005, Science 309:1519.