How does DNA-Directed RNA interference function?
DNA directed RNA interference (ddRNAi) relies on RNA polymerase III based promoters (e.g., U6 or H1) for the expression of siRNA target sequences that have been transfected in mammalian cells.
Pol III directs the synthesis of small RNA transcripts whose 3’ ends are defined by termination within a stretch of 4-5 thymidines. These characteristics allow for the use of DNA templates to synthesize, in vivo, small RNA duplexes that are structurally equivalent to active siRNAs synthesized in vitro.
Once transfected and transcribed in vivo, siRNA/RISC duplexes form in the cell and lead to the degradation of the target mRNA.
What are the formats of ddRNAi?
siRNA target sequences can be introduced into the cell by the generation of a ddRNAi expression cassette or by being cloned in a siRNA expression vector.
The following references review each of the formats in more detail.
