Editing Small interfering RNA (section)

==RNAi induction using siRNAs or their biosynthetic precursors==
[[Image:2ffl-by-domain.png|thumb|right|Dicer protein colored by [[protein domain]].]]
[[Gene knockdown]] by [[transfection]] of exogenous siRNA is often unsatisfactory because the effect is only transient, especially in rapidly dividing cells. This may be overcome by creating an [[expression vector]] for the siRNA. The siRNA sequence is modified to introduce a short loop between the two strands. The resulting [[Transcription (genetics)|transcript]] is a short hairpin RNA (shRNA), which can be processed into a functional siRNA by [[Dicer]] in its usual fashion.<ref>{{cite web|title=RNA Interference (RNAi)|url=http://www.sirnatransfection.org/rna-interference/|access-date=27 July 2018}}</ref> Typical transcription cassettes use an [[RNA polymerase III]] promoter (e.g., U6 or H1) to direct the transcription of small nuclear RNAs (snRNAs) (U6 is involved in [[Splicing (genetics)|RNA splicing]]; H1 is the [[ribonuclease|RNase]] component of human RNase P). It is theorized that the resulting siRNA transcript is then processed by [[Dicer]].

The gene knockdown efficiency can also be improved by using [[CellSqueeze|cell squeezing]].<ref name=pmid23341631>{{cite journal | vauthors = Sharei A, Zoldan J, Adamo A, Sim WY, Cho N, Jackson E, Mao S, Schneider S, Han MJ, Lytton-Jean A, Basto PA, Jhunjhunwala S, Lee J, Heller DA, Kang JW, Hartoularos GC, Kim KS, Anderson DG, Langer R, Jensen KF | display-authors = 6 | title = A vector-free microfluidic platform for intracellular delivery | journal = Proceedings of the National Academy of Sciences of the United States of America | volume = 110 | issue = 6 | pages = 2082–7 | date = February 2013 | pmid = 23341631 | pmc = 3568376 | doi = 10.1073/pnas.1218705110 | bibcode = 2013PNAS..110.2082S | doi-access = free }}</ref>
 
The activity of siRNAs in RNAi is largely dependent on its binding ability to the RNA-induced silencing complex (RISC). Binding of the duplex siRNA to RISC is followed by unwinding and cleavage of the sense strand with endonucleases. The remaining anti-sense strand-RISC complex can then bind to target mRNAs for initiating transcriptional silencing.<ref>{{cite journal |author=Daneholt, B. |title=Advanced Information: RNA interference |journal=The Novel Prize in Physiology or Medicine |year=2006}}</ref>