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What is RNAi ?

RNA interference, or RNAi, is thought to be a natural defense mechanism that has evolved for the protection of organisms from RNA viruses. Cells can recognize double stranded RNA (dsRNA) as an intruder. When this happens, the enzyme Dicer is recruited to cut the foreign RNA into smaller pieces called siRNA. These RNA pieces consist of approximately 22 nucleotides in length. One strand of the siRNA then binds to a target viral mRNA in a sequence-specific manner. This creates a signal for the destruction of the mRNA, thereby interfering with the further production of the viral proteins needed for a virus to replicate. To put it in other words, the RNA interference mechanism interferes with the expression of a particular gene that shares a sequence with the dsRNA that is homologous to that gene using certain fragments of double-stranded RNA to achieve this.

In 2006, Craig C. Mello and Andre Z. Fire were jointly awarded the "The Nobel Prize in Physiology or Medicine 2006" for their discovery of RNA interference - gene silencing by double-stranded RNA" 
http://www.nobelprize.org/nobel_prizes/medicine/laureates/2006/.

Their work demonstrated that double-stranded RNA (dsRNA) injected into the nematode worm C. elegans suppressed gene expression at a far higher potency than single-stranded RNA (ssRNA). The pathway by which dsRNA is able to silence gene expression has now been elucidated as RNAi and has been found to be widespread in eukaryotic organisms including humans.

The roundworm Caenorhabditis elegans is a free-living, non-parasitic, transparent nematode found in temperate soil environments. The worm is about 1 mm long and lacks a respiratory and a circulatory system and the majority of these worms are female hermaphrodites. Males have specialized tails for mating that include spicules, which are small or minute, slender, sharp-pointed body parts. C. elegans has been and still is being used as a model organism since Sydney Brenner began researching the molecular and developmental biology of this worm starting in 1974. The genomes for many worms including the genome of C. elegans as well as other pertinent data can now be found in public databases.


Links to Genomic Information
Wormbase:  
http://www.wormbase.org/species/c_elegans#140--10
Ensemble:  
http://www.ensembl.org/Caenorhabditis_elegans/Info/Index
Pubmed Genomes:  
http://www.ncbi.nlm.nih.gov/genome/?term=c+elegans