ON-TARGETTM plus技术
2006年Dharmacon公司在《Nature Methods》发表文章**证明基因沉默中脱靶效应的主要原因是siRNA序列中的“Seed Region”（反义链2－7核苷酸序列）活性所引起的1；因此，单独对正义链的修饰将无助于降低脱靶效应（见下图）。ON-TARGETplusTM 对siRNA双链同时进行修饰，是目前**能解决由siRNA双链所引起的脱靶效应一种修饰方式。
Figure: The ON-TARGETplus modification pattern dramatically reduces off-targets. Off-target effects induced by the indicated siRNAs were quantified using microarray analysis. For each target, three different siRNAs were used: unmodified, sense strand-inactivated, and ON TARGETplus-modified. Data shown represents genes down-regulated by two-fold or more. HEK293 cells were transfected with 100 nM siRNA using 0.2 µL of DharmaFECT® 1. Data was analyzed at 24 hours.
产品特点：
· 正义链的修饰阻止了其与RISC的互作，同时促进了反义链与RISC的相互作用。
· 通过修饰siRNA序列的Seed Region从而将于Seed Region相关的脱靶效应降到*低。
· 减少脱靶效应可达90％以上，大幅度降低了假阳性；增加了基因沉默实验可信度。
· 节省时间，并减少基因沉默中siRNA的筛选成本。
ON-TARGETplus siRNA同样建立于世界上*值得信赖的siRNA设计策略即SMARTselection™ 理性设计参数的基础上的。另外，Dharmacon公司*新突破的研究成果表明：siRNA的Seed Region和mRNA的3-UTR的匹配关系与基因沉默中的脱靶效应相关（见下图）2。ON-TARGETplus siRNA正是结合了这一发现并建立了全新的基因沉默标准，从而以**水平提高了siRNA的特异性。
Figure: Antisense strand seed regions contribute to off-target effects. A search for complementarity was performed between the siRNA antisense seed region (positions 2-7) and 5 UTRs, ORFs, and 3UTRs of off-targeted and unaffected (not silenced) genes. The number of seed matches to the 3UTR region is almost five-fold greater in the offtargeted genes than the unaffected genes.
综合上述研究成果的基础上，结合Dharmacon公司无可匹敌的生物信息学、****的化学修饰和已经广泛使用的Pool技术*终使得ON-TARGETplusTM siRNA成为真正意义上排除基因沉默中的脱靶效应的siRNA(图)。
Figure: Pooling of siRNAs reduces the overall number of off-targets. Off-target effects induced by the indicated siRNA reagents targeting 20 genes were quantified using microarray analysis. Data shown represents genes down-regulated by two-fold or more. Shaded box: Middle 50% of the data set. Line in box: Median value of the data set. Vertical bars: Minimum and maximum data values.
参考文献：
1. Jackson, A.L. et al."Position-specific Chemical Modification Increases Specificity ofsiRNA-mediated Gene Silencing." RNA 12.7(2006)1197-1205.
2. Birmingham, A., et al. "3-UTR seedmatches, but not overall identity, are associated with RNAi off-targets", Nature Methods. 3.3 (2006): 199-204.
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