Small interfering RNA (SI RNA)

Small interference RNA, or we can say these are the Double stranded RNA.

1. Small interfering RNA (Si RNA) Submitted to- Mr Samrat Chauhan Prepared by- Rishabh chalotra M. Pharmacy (Pharmacology) (M.M. college of pharmacy) 1

2. Contents Introduction History RNA interference Biosynthesis of Si RNA RNA interference Mechanism Significance of Si RNA Applications Conclusion 2

3. Introduction Also known to be short interfering RNA or Silencing RNA. These are a class of Double stranded RNA molecules. 20-25 base pairs in length. Similar to miRNA. (Micro RNA) 3

4. History The Nobel Prize in Physiology or Medicine 2006 was awarded jointly to Andrew Z. Fire and Craig C. Mello " for their discovery of RNA interference - gene silencing by double-stranded RNA. “ In 1998, the American scientists Andrew Fire and Craig Mello published their discovery of a mechanism that can degrade mRNA from a specific gene. 4

5. In 1990, plant biologist were trying to intensify the colour of the petals of Petunias, by introducing the formation of red pigment in the flower, but instead it turned it into white, the phenomenon was unable to explain until Fire and Mello made the discovery. Fire & Mello were investigating how gene expression is regulated in Nematode worm Caenorhabditis elegans. They inject mRNA molecule encoding protein led to no changes in the behaviour of the worm, the genetic code of mRNA is described as Sense sequence, and injecting antisense RNA, which can pair with mRNA , also had no effect. But when injected sense and antisense RNA together, they observe Unusual muscle contractions. 5

6. When sense and antisense RNA molecules meet, they bind to each other and form double-stranded RNA . After a series of experiments, Fire and Mello deduced that double-stranded RNA can silence genes. In every experiment, injection of double-stranded RNA carrying a genetic code led to silencing of the gene containing that particular code. The protein encoded by that gene was no longer formed. 6

7. RNA Interference (RNAI) Biological process in which RNA molecules inhibit gene expression, typically by causing the destruction of specific mRNA molecules. Phenomenon in which Double stranded RNA suppresses expression of a target protein by stimulating the specific degradation of the target mRNA . 7

8. Biosynthesis of Si RNA siRNA can be synthesized by using dsRNA obtained exogenously or endogenously. Endogenous: By transcription of both strands of DNA to form dsRNA. Exogenous: By the means of microinjecting dsRNA into the cell or by viral infections to the cell 8

9. RNA interference Mechanism Double stranded RNA (dsRNA) binds to the protein or emzyme Dicer. . It cleaves dsRNA into smaller fragments. One of the RNA strand is loaded into a RISC complex. It links the complex to the mRNA strand by base pairs. mRNA is cleaved and destroyed. No protein can be synthesized. 9

10. Significance of Si RNA RNAi protects against viral infection. RNAi secures genome stability by keeping mobile elements silent. RNAi-like mechanisms repress protein synthesis and regulate the development of organisms. RNAi-like mechanisms keep chromatin condensed and suppress transcription. RNAi offers a new experimental tool to repress genes specifically. RNAi might be a useful approach in future gene therapy. 10

11. Applications Basic research - Determining protein function - Easier than a knockout and may be used for partial knockdowns. Clinical research - Cancer, hypercholesterolemia, infections, developmental defects 11

12. Conclusion RNAi is an important part of the cellular machinery that provides viral immunity and mechanism for the control of gene expression. siRNA triggers function in the RNAi mechanism result in gene suppression. Potential therapeutic application include viruses and cancer. Technical challenges: Stability, Targeting, Off-target, effects, Immune response, Delivery. The field is relatively young and much remains to be discovered. 12

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