In a paper published in the February 2008 issue of RNA, a group of researchers has shown1 that 5’-OMe modification of a strand of a ds-siRNA can control guide strand selection and targeting specificity.
It is known that siRNA- and miRNA-containing ribonucleoprotein silencing complexes (RISC) are formed from short double-stranded RNA. Duplex siRNA is basically symmetric. However, only one strand enters the RISC and there is a bias for the preferred loading of one of the two duplex-forming strands into the RISC. Recruitment of the “wrong” strand can reduce expected activity and generate off-target silencing.
In their RNA paper, the authors have shown that the 5’-phosphorylation status within a duplex siRNA is an important determinant of strand incorporation into RISC. They also demonstrated that selective asymmetric 5’-O-methylation of one strand of an siRNA duplex can be used to direct the non-methylated strand to be incorporated into RISC. The off-targeting activity of the 5’-O-methylated strand was reduced, while the off-targeting activity of the phosphorylated strand was enhanced. They concluded that asymmetric 5’ modification of siRNA duplexes can be extremely useful for controlling targeting specificity.
This simple and effective modification of siRNA can be readily achieved using our product (5’-O-Me-dT phosphoramidite; 10-1031).