title: Strand-specific 5'-O-methylation of siRNA duplexes controls guide strand selection and targeting specificity.
abstract: Small interfering RNAs (siRNAs) and microRNAs (miRNAs) guide catalytic sequence-specific cleavage of fully or nearly fully complementary target mRNAs or control translation and/or stability of many mRNAs that share 6-8 nucleotides (nt) of complementarity to the siRNA and miRNA 5' end. siRNA- and miRNA-containing ribonucleoprotein silencing complexes are assembled from double-stranded 21- to 23-nt RNase III processing intermediates that carry 5' phosphates and 2-nt overhangs with free 3' hydroxyl groups. Despite the structural symmetry of a duplex siRNA, the nucleotide sequence asymmetry can generate a bias for preferred loading of one of the two duplex-forming strands into the RNA-induced silencing complex (RISC). Here we show that the 5'-phosphorylation status of the siRNA strands also acts as an important determinant for strand selection. 5'-O-methylated siRNA duplexes refractory to 5' phosphorylation were examined for their biases in siRNA strand selection. Asymmetric, single methylation of siRNA duplexes reduced the occupancy of the silencing complex by the methylated strand with concomitant elimination of its off-targeting signature and enhanced off-targeting signature of the phosphorylated strand. Methylation of both siRNA strands reduced but did not completely abolish RNA silencing, without affecting strand selection relative to that of the unmodified siRNA. We conclude that asymmetric 5' modification of siRNA duplexes can be useful for controlling targeting specificity.
authors: Laboratory of RNA Molecular Biology, Howard Hughes Medical Institute, The Rockefeller University, New York, New York 10021, USA.
authors: Po Yu
authors: PY
authors: Chen
authors: Lasse
authors: L
authors: Weinmann
authors: Dimos
authors: D
authors: Gaidatzis
authors: Yi
authors: Y
authors: Pei
authors: Mihaela
authors: M
authors: Zavolan
authors: Thomas
authors: T
authors: Tuschl
authors: Gunter
authors: G
authors: Meister
mesh_terms: D000818:Animals; D001483:Base Sequence; D008745:Methylation; D008969:Molecular Sequence Data; D009154:Mutation; D010710:Phosphates / Q000737:chemistry / Q000378:metabolism*; D010766:Phosphorylation; D034622:RNA Interference; D034741:RNA, Small Interfering / Q000378:metabolism*; D034743:RNA-Induced Silencing Complex / Q000737:chemistry / Q000378:metabolism*
chemical_list: D010710:Phosphates; D034741:RNA, Small Interfering; D034743:RNA-Induced Silencing Complex