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RNAi Mechanism INTERFERENCE.... The Central Dogma DNA (double-stranded) RNA (single-stranded) Protein When good RNA goes bad.... Viruses can make doublestranded RNA How did cells evolve to fight this? When good RNA goes bad.... Cells sense doublestranded RNA and activate a response called RNAi Understanding how RNAi works is the key to using it as a genetic tool and for therapy Dicer cuts dsRNA into short RNAs Vanhecke, D.; Janitz, M. Drug Discov. Today, 2005, 10, 205-225. Role for a bidentate ribonuclease in the initiation step of RNA interference Emily Bernstein, Amy A. Caudy, Scott M. Hammond & Gregory J. Hannon 2001 Bernstein et al. Cloned Dicer, the RNase III enzyme that is evolutionarily conserved and contains helicase and PAZ domains, as well as two dsRNA-binding domains. RNAi functions in many different organisms dsRNA How do small dsRNAs turn genes off? Model for translational repression M7GpppG RISC recognizes a target RISC AAAAAA......... Model for translational repression M7GpppG DCP GW RISC Other proteins are also recruited – either along with RISC or later other AAAAAA......... Least well understood - Arabidopsis as a model….