Many researchers today employ synthetic 21-mer RNA duplexes as their RNAi reagents, which mimic the natural siRNAs that are the result of Dicer processing of long substrate RNAs.
An alternative approach is to use synthetic RNA duplexes (DsiRNAs) that are greater than 21-mer in length, which are substrates for Dicer.
DsiRNAs are processed by Dicer into 21-mer siRNAs and designed so that cleavage results in a single, desired product.
This DSiRNA design provides Dicer with a single favorable PAZ binding site that helps direct the cleavage reaction. Functional polarity is introduced by this processing event, which favors AS strand loading into RISC, and the increased potency of these reagents is thought to relate to increased DSiRNAs being loaded into and processed through Dicer.
The Dicer-substrate approach can result in reagents having as much as 10-fold higher potency than traditional 21-mer siRNAs at the same site.