In a study of patients with non-Hodgkin B cell lymphoma, a nuclear gene is found to be actively transcribed to mRNA and is transported into the cell cytoplasm. A protein is translated from this mRNA, with up-regulation of BCL2. In a control group without lymphoma, translation of the mRNA does not occur. How is the silencing of this active gene's mRNA most likely to occur?

MicroRNAs (miRNAs) are encoded by about 5% of the human genome. miRNAs do not encode for proteins, but bind and inactivate or cleave mRNA, preventing translation of proteins by mRNA. This effectively silences gene expression without affecting the gene directly. There is abundant transfer RNA (tRNA) present in the cytoplasm that is not a rate-limiting step to translation. DNA methylation, particularly at CG dinucleotides, is a way of suppressing gene expression directly, as is seen with genomic imprinting. Mutations that occur in genes in DNA may result in reduced mRNA production or abnormal protein production, but mRNA itself is not mutated. Mitochondrial DNA (mtDNA) encodes for proteins that are mainly involved in oxidative phosphorylation metabolic pathways