siRNA - sh and si RNA RJNAi (Jul/26/2006 )

hi I am confuse about siRNA

so many designations as shRNA,siRNA, RNAi

is it the same? what are their realtionships?

thanks

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RNAi: RNA antisense that is complementary to the sense mRNA
siRNA: small RNAi, 21-23 nucleotides long (you can see it as a small piece of the RNAi)
shRNA: short hairprin RNA (it forms a hairprin structure)

Does it help?

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I don't think RNAi is antisense I think its RNA interference.
well what is the relationship between them?especially between shRNA and siRNA




RNAi: RNA antisense that is complementary to the sense mRNA
siRNA: small RNAi, 21-23 nucleotides long (you can see it as a small piece of the RNAi)
shRNA: short hairprin RNA (it forms a hairprin structure)

Does it help?
[/quote]

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Yes, to be precise and correct the RNAi is the mechanism by which dsRNA is degraded. You can do it using a long antisense RNA that some people call RNAi to distinguish it from the siRNA.
You can visit this:
http://www.nature.com/focus/rnai/animations/index.html

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shRNA is what is cloned into a vector and when these vectors r transfected, the shRNA is expressed and is cleaved into small siRNA in the cell.

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you are right about RNAi this refers to the general idea/method know as RNA interference

to understand the differences between siRNA and shRNA, you need to look at how RNAi works.

Namely, the apperance of dsRNA in the cell causes the cascade of events know as RNAi
the difference between the 2 is as follows

siRNA: these are small RNA fragments 22-24 bp that have been cleaved and either by the dicer enzyme post binding or introduced into the cell, importantly they recognise existing cellular RNA and bind to it forming a dsRNA, which activates RNAi

shRNA: these are small RNA that are palindromic, and thus can fold back on themselves to forming hairpin structures, thus they can form dsRNA without the need for an existing cellular target, again these dsRNA structures activate RNAi via incorportation into dicer enzyme.

both are different techniques that can be used in RNAi, for example by introducing a shRNA that shares sequence with a know gene, by continually expressing the shRNA you are continually priming the cell against that specific mRNA being able to be produced.

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RNAi is a biological pathway for gene silencing in a sequence spesific manner. The siRNA derived from DICER activity. Diser is able to generate siRNA from double-strand RNA.
shRNA is a component of the miRNA (small non coding RNA) pathway. In the last years shRNA are used for siRNA delivery in cells (Vectors for shRNA expression are developed and they are provided by different company).

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