Figure 1

Model of microRNA (miRNA) biogensis/transportation/function. In the nucleus, miRNA are transcribed by RNA polymerase II into single strand RNA, which folds into a double stranded primary miRNA (pri-miRNA). Pri-miRNA are cleaved by Drosha yielding the precursor miRNA (pre-miRNA). Pre-miRNA are then translocated from the nucleus via exportin 5 to the cytoplasm. Once in the cytoplasm pre-miRNA are further cleaved by the RNase III endonuclease Dicer into a double stranded miRNA. Only one strand of the duplex is stably associated with the miRISC complex. The miRNA strand is usually favoured more than the miRISC* strand, although there are exceptions. The double stranded miRNA then separates into two single strands, one strand is then degraded and the other is incorporated into a complex with argonaute proteins, forming the RNA induced silencing complex (RISC). RISC then binds to target mRNA causing translational repression or degradation. Adapted and modified from [7].