My textbook says that in RNAi, a complementary double stranded RNA sequence attaches to an mRNA and silences it using a protein machinery. I Googled and read about this so now I know what siRNA and RISC and microRNA are. But the next thing my book says is

the source of these complementary double stranded RNA sequence [obviously my textbook means siRNA] may be viruses and transposable elements.”

What does this mean? Do transposons make siRNA? I thought transposons were non-coding except when they travel via the retrotransposon mechanism.

Do viruses that infect eukaryotic cells donate their own RNA genetic material for the cell to use in RNAi? But I thought RNAi was a cellular defence against viruses, how can viruses help give the dsRNA that’s supposed to fight the viruses? A number of sites online simply state that siRNA is exogenous is origin; do they mean that it comes from viruses?

I would greatly appreciate it if someone could take the time to answer each of my questions one by one or even recommend a site that answers them all.


Transposons and viruses don't "make siRNA". However, an endonuclease called Dicer can process dsRNA from these sources to produce siRNA which is then loaded to the RNA-induced silencing complex (RISC) to suppress propagation of viruses and transposons. The following papers provide a good overview:

Buchon N, Vaury C. 2006. RNAi: a defensive RNA-silencing against viruses and transposable elements. Heredity 96:195-202.

van Rij RP, Andino R. 2006. The silent treatment: RNAi as a defense against virus infection in mammals. Trends Biotechnol 24:186-193.

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  • $\begingroup$ Not sure how much of an explanation you are looking for since this is well covered on Wikipedia and in scientific literature. If you want me to elaborate on something, let me know. $\endgroup$ – canadianer Oct 6 '17 at 18:24
  • $\begingroup$ Thank you for the site-links, I read them and it’s safe to say, I have a fair idea now. $\endgroup$ – Inkjet Oct 8 '17 at 9:01

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