Editing Small interfering RNA (section)

== Structure ==
[[File:SiRNA Structure2.svg|thumb|right]]
Naturally occurring siRNAs have a well-defined structure that is a short (usually 20 to 24-[[base pair|bp]]) [[double-stranded RNA]] (dsRNA) with [[phosphorylation|phosphorylated]] 5' ends and [[hydroxylation|hydroxylated]] 3' ends with two overhanging nucleotides.
The [[Dicer]] [[enzyme]] catalyzes production of siRNAs from long [[dsRNA]]s and [[small hairpin RNA]]s.<ref>{{cite journal | vauthors = Bernstein E, Caudy AA, Hammond SM, Hannon GJ | author-link1=Emily Bernstein|title = Role for a bidentate ribonuclease in the initiation step of RNA interference | journal = Nature | volume = 409 | issue = 6818 | pages = 363–6 | date = January 2001 | pmid = 11201747 | doi = 10.1038/35053110 | s2cid = 4371481 | bibcode = 2001Natur.409..363B }}</ref> siRNAs can also be introduced into cells by [[transfection]]. Since in principle any gene can be [[Gene knockdown|knocked down]] by a synthetic siRNA with a complementary sequence, siRNAs are an important tool for validating gene function and drug targeting in the post-genomic era.