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1: RNA. 2006 Jul;12(7):1197-205. Epub 2006 May 8.
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Position-specific chemical modification of siRNAs reduces "off-target" transcript silencing.

Jackson AL, Burchard J, Leake D, Reynolds A, Schelter J, Guo J, Johnson JM, Lim L, Karpilow J, Nichols K, Marshall W, Khvorova A, Linsley PS.

Rosetta Inpharmatics, LLC, Seattle, WA 98109, USA. aimee_jackson@merck.com

Transfected siRNAs regulate numerous transcripts sharing limited complementarity to the RNA duplex. This unintended ("off-target") silencing can hinder the use of RNAi to define gene function. Here we describe position-specific, sequence-independent chemical modifications that reduced silencing of partially complementary transcripts by all siRNAs tested. Silencing of perfectly matched targets was unaffected by these modifications. The chemical modification also reduced off-target phenotypes in growth inhibition studies. Key to the modification was 2'-O-methyl ribosyl substitution at position 2 in the guide strand, which reduced silencing of most off-target transcripts with complementarity to the seed region of the siRNA guide strand. The sharp position dependence of 2'-O-methyl ribosyl modification contrasts with the broader position dependence of base-pair substitutions within the seed region, suggesting a role for position 2 of the guide strand distinct from its effects on pairing to target transcripts.

PMID: 16682562 [PubMed - indexed for MEDLINE]

PMCID: PMC1484422