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. 2021 Aug 17;12(17):1707–1723. doi: 10.18632/oncotarget.28039

Figure 1. Biogenesis and clinical implications of microRNAs (miRNAs).

Figure 1

(A) miRNA genes are typically transcribed by RNA polymerase-II and produce long primary miRNA (pri-miRNA), which are recognized and cleaved in the nucleus by the RNA polymerase III enzyme Drosha. (B) Next, pri-miRNA is processed to precursor miRNA (pre-miRNA) hairpin like structure in the nucleus by the Drosha/Pasha complex, are then transported into the cytoplasm by Exportin 5 and further is processed by another RNase enzyme called Dicer, produce miRNA duplexes. (C) The miRNA duplexes (miRNA:miRNA* duplexes shown in blue color) are then unwound and the guide strands are selected by Argonaute for integration into the RNA induced silencing complex (RISC). (D) The mature miRNA leads RISC to cleave the mRNA or induce translational repression depending on the degree of the miRNA and its target genes. Figure was reproduced with permission of Dr. Ahir [31].