Figure 3. Gene suppression. A: Zinc finger artificial transcription factors (ZF-ATF) use suppressor transcription factors to silence gene transcription. B: Zinc finger nucleases (ZFN) causes a double-stranded break leading to correction of the mutation through recombination. C: miRNA and shRNA degrade the endogenous target transcript while sparing the introduced resistant mRNA (hardened) with an altered sequence. D: Ribozymes catalytically cleave the target transcript, but insertion of a guanosine at the target site dramatically reduces cleavage of the hardened target.