INTRODUCTION:
RNA interference is a rapidly emerging and powerful technique which is used to turn off the activity of specific target gene. This is used to investigate gene function by degrading the specific mRNA target in a particular cell by utilizing short double standard RNA prior to translation.

HISTORY:
This biological process was first observed in plants when the plant biologist Rich Jorgensen was working on petunias for getting more intense purple colour by introducing exogenous transgenes. Instead of intensifying the colour, the resulting flowers had white patches. This phenomenon was referred to co-suppression.

At the same time some observations were obtained and those were related to plant responses when they were infected by the viruses. The viral RNA was degraded by plants. This phenomenon was referred to Post Transcriptional Gene Silencing or Virus Induced Gene Silencing.
This biological process was first observed in plants when the plant biologist Rich Jorgensen was working on petunias for getting more intense purple colour by introducing exogenous transgenes. Instead of intensifying the colour, the resulting flowers had white patches. This phenomenon was referred to co-suppression.

At the same time some observations were obtained and those were related to plant responses when they were infected by the viruses. The viral RNA was degraded by plants. This phenomenon was referred to Post Transcriptional Gene Silencing or Virus Induced Gene Silencing.

Guo and Kemphues in 1995 found that the Sense and Antisense RNA were equally effective in inhibition of gene expression in Caenorhabditis elegans (a nematode).Then Endrew Fire and Craig C. Mello continued this work and They observed that in C. elegans, double stranded DNA was highly strong at suppressing gene expression. Then their work was reported as a paper in 1998 and for this discovery, they were awarded Nobel Prize in Physiology or Medicine.

After the report of Endrew Fire and Craig C. Mello, RNA interference has been reported in a majority of the organisms which include hydra, fungi, zebrafish, planaria, , drosophila & mice. Such silencing of the gene by introducing transgenic copy of a particular gene was termed quelling in Neurospora crassa.

MECHANISM:
After the synthesis of double stranded RNA (by joining sense and antisense RNA together), it is recognised by an enzyme namely Dicer i.e. a member of RNAse III family. This enzyme cleaves the longer ds RNA and stem loop ds RNA into short fragments around 21-23 nucleotides i.e. small interfering RNA(si RNA) and micro RNA(miRNA) respectively. Both these reactions are ATP dependent.
These siRNAs are then incorporated into a targeting complex i.e. RISC(RNA Induced Silencing Complex) that includes the member of argonaute family of proteins. These proteins are the essential components of RNA interference machinery. RISC destroys another cellular mRNA and results in rapid degradation of target mRNA and leads to decrease in gene expression.

Such systematic silencing has been noticed in plant and is known as transitive RNA interference. Transitive RNA interference refers to the movement of RNA silencing signal along a particular gene.

APPLICATIONS IN TREATMENT OF HUMAN DISEASES:
RNA interference has several potential applications not only in gene function analysis but also in therapeutics. It is being used in the treatment of various kinds of cancers by using siRNA specific for oncogene silencing. For example in case of Lymphoblastic leukemia, Pancreatic and colon carcinomas etc. it is also being used in the treatment of HIV by the down regulation of cellular co factors required for HIV infection.

It is also being used in the treatment of viral hepatitis, malaria, ocular diseases, cardiovascular and cerebral vascular diseases, metabolic diseases and neurodegenerative disease etc.

FUTURE ASPECTS:
It is very promising new tool for treating various kind of genetic disorders. This technology has been opening new vistas for further studies toward novel gene therapy approaches for anticancer and antiviral treatments.

CONCLUSION:
The discovery of RNA interference has taken the scientific world in a new era where functional analysis of genes can be precisely carried out using these small RNA molecules. RNA interference is a key breakthrough of last decade which will revolutionize genetic, genomic and proteomic aspects and will lead to a new era in field of therapeutics.

About Author / Additional Info:
1. RNA Interference: Biology, Mechanism, and Applications
Malhotra, Raj K. Bhatnagar and Sunil K. Mukherjee Neema Agrawal, P. V. N. Dasaradhi, Asif Mohmmed, Pawan
2. RNA Interference (RNAi)
www.stanford.edu/gro up/ho pes/cgi-bin/wordpress/2010/06/rna-interference-rnai/
3. RNAi: RNA Interference
By Natalie Betz, Ph.D., Promega Corporation