Any of several types of small RNA molecules that are produced in cells from double-stranded (ds) precursors by the action of the protein Dicer. This cuts the precursor to form a single-stranded RNA, typically 21 or 22 nucleotides long, that binds to sites with the complementary sequence on messenger RNA (mRNA) molecules, thereby triggering degradation of the mRNA. This mechanism of RNA interference probably evolved as a means of combating infection by RNA viruses, which replicate via double-stranded RNA intermediates. dsRNA can also be introduced by transfection of cells; this is performed experimentally to silence particular genes using siRNAs designed to bind to specific mRNAs. The base sequence of siRNAs matches perfectly that of their binding site and triggers cleavage of the target RNA, whereas microRNAs, which are normally encoded by the cell to control gene expression, often bind their targets imperfectly and merely suppress translation of the mRNA.
Subjects: Biological Sciences.