RNA

The term RNA interference (RNAi) was coined to describe a cellular mechanism that use the gene's own DNA sequence of gene to turn it off, a process that researchers call silencing. In a wide variety of organisms, including animals, plants, and fungi, RNAi is triggered by double-stranded RNA (dsRNA).

During RNAi, long dsRNA is cut or "diced" into small fragments ~21 nucleotides long by an enzyme called "Dicer". These small fragments, referred to as small interfering RNAs (siRNA), bind to proteins from a special family    the Argonaute proteins. After binding to an Argonaute protein, one strand of the dsRNA is removed, leaving the remaining strand available to bind to messenger RNA target sequences according to the rules of base pairing    A binds U, G binds C, and vice versa. Once bound, the Argonaute protein can either cleave the messenger RNA, destroying it, or recruit accessory factors to regulate the target sequence in other ways.

RNAi is widely used by researchers to silence genes in order to learn something about their function. siRNAs can be designed to match any gene, can be manufactured cheaply, and can be readily administered to cells. One can now order commercially synthesized siRNAs to silence virtually any gene in a human or other organism's cell, dramatically accelerating the pace of biomedical research. Furthermore, the ability to turn off expression of a single gene makes RNAi an appealing therapeutic approach to treat infectious diseases or genetic disorders, such as those that result from the inappropriate and undesirable activity of a gene, as in many cancers and neurodegenerative diseases. There are currently several clinical trials testing the safety and effectiveness of siRNA drugs.