One of the fastest and easiest ways to silence genes in cells and organisms is via RNA interference (RNAi). Discovered in 1998, RNAi exploits a natural mechanism used in a wide variety of plants and animals to protect themselves against infection with certain viruses and the proliferation of mobile genetic elements. The technique involves introducing into a cell or organism double-stranded RNA molecules with a nucleotide sequence that matches the gene to be inactivated.

The double-stranded RNA is cleaved and processed by special RNAi machinery to produce shorter, double-stranded fragments called small interfering RNAs (siRNAs). These siRNAs are separated to form single-stranded RNA fragments that hybridize with the target gene’s mRNAs and direct their degradation. In some organisms, the same fragments can direct the production of more siRNAs, allowing continued inactivation of the target mRNAs.