Why use a pol III type promoter?
For efficient shRNA expression a pol III type promoter is used. These Pol III promoters contain all of their essential elements upstream of the expressed RNA and terminate with a short polythymidine tract. Once the shRNA is expressed, it is transported from the nucleus and processed into siRNA in the cytoplasm by the enzyme Dicer. Dicer preferentially recognizes shRNA generated from a pol III promoter because they carry no 5’ or 3’ flanking sequences. The siRNA enters into RISC complexes and generates an RNAi response in mammalian cells.
