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. Author manuscript; available in PMC: 2011 Dec 1.
Published in final edited form as: FEBS J. 2010 Dec;277(23):4806–4813. doi: 10.1111/j.1742-4658.2010.07903.x

Figure 1. Key design options for siRNAs.

Figure 1

siRNAs can be modified on either their guide (red) or passenger (blue) strands. Multiple chemical modifications can be made along the length of the siRNA or at the termini as discussed elsewhere [50, 51], including modifying the backbone, base, and terminal chemistry, especially of the passenger strand. Formation of intramolecular secondary structure by the guide strand after separation from the passenger strand has also been examined as a design criterion [32–34]. Although positional base preferences have been suggested for multiple locations along the siRNA (e.g. [28]), this review focuses primarily on the characteristics of the siRNA termini, hybridization asymmetry and sequence (i.e., the 5′-nucleotide on each strand), for use in the design of highly active siRNAs.