siRNA vs miRNA - why multiple terms for literally the same process? - (Feb/06/2007 )

I have been trying to determine why we have so many terms for a process that is relatively the same.

For example, I have no idea what's the difference between siRNA and microRNA (miRNA) - both are formed from dsRNA and both eventually get cleaved into pieces by Dicer and then incorporated into RISC which in effect cleaves target mRNA.

Any clarification to this would be appreciated! Thanks!

siRNA and microRAN are not the exact same thing and they differ in many ways.

siRNA usually refers to synthetic or exogenous dsRNA of ~21-nt in size, which forms the RISC complex with Ago2 and cleaves its target mRNA if it has perfect complementarity with its target.

microRNA is generated within the cell, highly conserved, rarely has perfect complementarity with mRNA sequences, but it can affect protein translation and mRNA decay by binding to its imperfectly matched target sites on 3' UTR region of a mRNA, which als requires Ago protein (not necessarily Ago2).

If an siRNA hits a imperfect complementary target on 3 UTR, it behaves similar to microRNA, if a microRNA hits a perfectly matched target on a mRNA, it can behave like an siRNA.

So they are very different but also very similar.

Hope that helps.

But don't forget that miRNAs show heteroduplex structures and siRNAs not.

both are used for gene inactivation