RNA interference

RNA interference (RNAi; post-transcriptional gene silencing) The ability of double-stranded RNA to interfere with, or suppress, the expression of a gene with a corresponding base sequence. The phenomenon occurs in many types of organisms, including plants, fungi, and animals. Double-stranded RNA, which is normally a rarity in cells, is cut into fragments by a ribonuclease enzyme (e.g. Dicer in Drosophila). The fragments, typically 21–25 bp long, are called short interfering RNA (siRNA). The two strands of each fragment partially separate, allowing the antisense strand to bind to a complementary ‘sense’ region of another RNA molecule, such as a messenger RNA (mRNA). This then triggers cleavage of the mRNA at that site, thereby effectively blocking expression of the corresponding gene. It is thought that RNA interference may be a mechanism for the cell to combat infection by certain RNA-containing viruses. Alternatively, the cell may use short single-stranded RNAs, called microRNAs (miRNAs), as a means of regulating gene expression, by effectively targeting certain mRNAs for destruction or by repressing their translation. RNA interference is now used as a powerful and versatile experimental tool to suppress particular genes, as a form of knockout.