fig1

Figure 1. The biosynthesis of miRNAs begins in the nucleus. RNA polymerase (RNA pol) transcribes primary miRNAs, which consist of a poly-A tail and a 5’ cap. The multi-processor complex made up of double-stranded-RNA-binding protein and the RNase III enzyme Drosha to form pre-miRNAs. The Ran-GTP complex and karyopherin export pre-miRNAs into the cytoplasm. To finalize the process, the RNase III enzyme Dicer cleaves pre-miRNAs and triggers a further processing step by generating the miRNA. When miRNA-induced silencing complex (miRISC) is in the cytoplasm, miRNAs act on the target transcripts via complementary Watson-Crick base pairing to the corresponding miRNA response elements (MREs), which are usually present within the 3ʹ-untranslated regions (3’UTRs) of target genes. Upon binding to MREs within 3’UTRs, miRNAs reduce protein outcome from the target transcripts due to translational repression and/or mRNA deadenylation and decay mechanisms