Isonucleotide incorporation into middle and terminal siRNA duplexes exhibits high gene silencing efficacy and nuclease resistanceElectronic supplementary information (ESI) available. See DOI: 10.1039/c7ob01065f

• Main Authors: Ma, Yuan, Liu, Shuang, Wang, Yusi, Zhao, Yuanhe, Huang, Ye, Zhong, Lijun, Guan, Zhu, Zhang, Lihe, Yang, Zhenjun
• Format: Article
• Language: English
• ISSN: 1477-0520; 1477-0539
• DOI: 10.1039/c7ob01065f

In this study, we introduced a pair of nucleotide enantiomers, d -/ l -isonucleotides ( d -/ l -isoNA), to examine the interactions between siRNAs and their related proteins. The serum stability and gene-silencing activity of the modified siRNAs were systematically evaluated. Gene-silencing activity had a site-specific effect, and the incorporation of a single d -isoNA at the 8th position (counting from the 5′-terminus) in the antisense strand improved the gene-silencing activity by improving RISC loading and affecting the movement of the PIWI domain. d -isoNA incorporated at the terminus of siRNA including the 2nd position in the antisense strand and 3′-overhangs in the sense strand, especially the latter, enhanced nuclease resistance and prolonged the silencing retention time. In addition, l -isoNA incorporation into the middle of the sense strand enhanced activity. These results provide a chemical strategy for the modulation of siRNA gene-silencing activity and nuclease resistance. d -/ l -Isonucleotides were used to explore the local conformation requirement at specific sites of siRNA; both silencing activity and nuclease resistant character were improved, respectively.