FIG. 4.

The mammalian RNA silencing pathway. The diagram summarises the major features of the RNA silencing pathway in mammalian cells. The pink boxes on the right represent the endogenous miRNA pathway, while the blue boxes on the left indicate the points at which the endogenous silencing pathway can be subverted to produce knockdown of specified target mRNAs. Artificial miRNA-like constructs, known as shRNA-miRs, are transcribed from RNA Pol II or III promoters and enter the miRNA pathway at the start. Artificial shRNAs are generally expressed from RNA Pol III promoters and enter the miRNA pathway at the Dicer stage. Lastly, conventional ∼21–23 nucleotide siRNAs only need to be unwound in the cytoplasm before they enter the RISC to mediate gene silencing. Color images available online at www.liebertpub.com/hgtb