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What is the difference between ON-TARGET, ON-TARGETplus, siSTABLE, and unmodified siRNA duplexes? When should I use the modified versions?

ON-TARGET siRNA duplexes are modified so that sense strand interactions with the RISC are impaired and interactions with the antisense (silencing) strand are favored. When using siRNA-mediated silencing in organisms with a well-defined genome, this is usually not necessary as we can eliminate off-target effects associated with the sense strand using careful bioinformatic screens. However, in cases where the genome is incomplete or when the only options available for a functional siRNA include the possibility of sense strand-induced silencing, ON-TARGET modification should be considered. ON-TARGETplus siRNA incorporates the ON-TARGET modification plus an additional modification to improve specificity of antisense strand binding to its target. This modification is the most comprehensive for combating off-target effects. siSTABLE duplexes are modified to confer resistance to degradation by nucleases that can occur extracellularly or intracellularly. These duplexes should be considered for use when working with in vivo models or other systems that may expose the siRNA to a high nuclease environment. Unmodified siRNA duplexes do not carry any chemical modifications.

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