RISC RNAi-induced silencing

Fig. 3.2 (A) The RNAi pathway Dicer with its RNAse III domains cleaves long double-stranded RNA (dsRNA) twice per strand, and generates the siRNA duplex. After cleavage, a siRNA/protein complex (siRNP) is formed. In the next step, the siRNA is unwound and the RNA-induced silencing complex (RISC) becomes activated. The target...

Not all siRNAs are created equal and a major effort has been made to determine the best siRNAs to knockdown a gene of interest. Understanding the next step in the RNAi pathway downstream of Dicer has proven very helpful in this respect. The siRNA molecules generated by Dicer become incorporated with the RNA-induced silencing complex (RISC) that uses the short RNA as a template to target an mRNA species for cleavage and eventual degradation (35). However, each RISC complex contains only one strand of ssRNA from the siRNA duplex (36) therefore, to produce an effective knockdown, it must incorporate... 

FIGURE 15.2 The mechanism of RNA interference (RNAi). Exogenous double stranded RNA or endogenous hairpin RNA is cleaved by Dicer to make short interfering RNAs (siRNAs). These are incorporated into the RNA-induced silencing complex (RISC). Upon activation with ATP, the siRNA unwinds and the RISC complex mediates the cleavage of the target mRNA. 

The release of nucleic acid drugs is essential for the active function of nucleic acid drugs. The RNA interference (RNAi) activity of siRNA delivered by a reducible poly(amido ethylenimine) (SS-PAEI) was significantly higher than that of linear PEI [181]. The fast degradation of disulfide bonds in the SS-PAEI backbone and the resulting efficient release of siRNA can increase the bioavailability of siRNA and its accessibility to RNA-induced silencing complex (RISC), whereas linear PEI-siRNA complexes maintained their ordered structure even at 5 h after cytosolic internalization. 

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