Advances in Chemical Modification of siRNA siRNA, with a molecular weight of about 13 kDa, recruits the RNA-induced silencing complex (RISC) to mRNA through base pairing, thereby inhibiting protein translation (Fig. 1). The mRNA is targeted for cleavage through the catalysis of the RISC protein Ago2, a member of the Argonaute family. In addition, other Ago proteins (Ago1, Ago3, and Ago4) catalyze endonuclease-mediated degradation of...