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Illustration of a pre-miRNA (precursor micro ribonucleic acid, red) being exported through a nuclear pore complex (NPC, blue and white) in a cell's nuclear envelope by the exportin-5(white)/RanGTP(light violet)-complex. The pre-miRNAs are processed to miRNAs once in the cytoplasm. miRNAs act to inhibit the expression of specific genes by regulating the expression of messenger RNA (mRNA). NPCs are complexes of proteins that are embedded in the nuclear envelope. All material moving between the nucleus and the cytoplasm passes through these channels. They allow passive transport (diffusion) of ions and small molecules and active transport (energy dependent) of proteins and RNAs (ribonucleic acids)