RNA-Interference

Andrew Fire and Craig Mello 2006 (Nobel Prize in Physiology or Medicine of the Year 2006)

RNA interference, or RNAi for short, refers to an interruption of translation, i.e. the translation of the messenger RNA(mRNA) into a protein. The organism uses RNA interference and RNA silencing to regulate its gene expression, for example to ward off invading foreign nucleic acids (e.g. viruses). This "tool" is developed in all eukaryotic cells. RNA interference is therefore a form of gene regulation in which an already transcribed gene is not converted into a protein, or only to a small extent (gene silencing). As RNA interference usually occurs after transcription, it is also referred to as "post-transcriptional gene silencing" (PTGS).

During gene silencing, double-stranded RNA molecules are formed in the cell, which are cleaved by dicers (dsRNA-specific endonucleases from the RNase III family), into small RNAs with a length of 18-25 nucleotides. These molecules are also known as siRNAs (small interfering RNAs) or micro RNA (miRNA). The siRNAs are then incorporated as a single strand by a Dicer-associated protein into the RNA-induced silencing complex(RISC), which contains so-called Argonaute proteins and can degrade RNA that is complementary to the siRNA - the siRNA thus formally corresponds to an antisense mRNA.

The best-known RNAi is rather short (only around 20 base pairs long) and combines with the Argonauts (special proteins) to regulate genes - in most cases to silence them. Actually, the Argonauts do all the work, they are just directed to the right place by the RNAi. The RNAi find their complementary mRNA, the Argonauts chop it up and render it useless.

1. Agrawal N et al. (2003) RNA interference: biology, mechanism, and applications. Microbiol Mol Biol Rev 67:657-685.
2. Han H (2018) RNA interference to knock down gene expression. Methods Mol Biol 1706:293-302.