{"doi":"10.1093/nar/gkaf1438","title":"Presence of phosphodiester backbone, but not nucleobases, in the guide’s 3′ terminal region is necessary for RISC loading and target cleavage <i>in vitro</i> and <i>in vivo</i>","abstract":"Short interfering RNAs (siRNAs) represent a novel class of therapeutic modalities, where, in the context of complex chemical modification patterns, a single administration can support sustained gene silencing. Various siRNA architectures demonstrate robust activity; however, a guide strand length of 19-21 nucleotides is generally believed to be required for effective gene silencing. Here, we show that up to five terminal positions of the guide strand can be efficiently substituted with non-nucleobase-containing analogs without a measurable loss of activity in vitro or in vivo. While nucleobases are not essential at these positions, the presence of a phosphodiester backbone is critical. Both the distance between phosphate groups and the lipophilicity of the phosphodiester-linking analogs significantly influence silencing activity. Longer carbon-based chains reduce activity, whereas ethylene glycol-based chains preserve activity, highlighting the importance of backbone architecture in RISC engagement. These findings demonstrate that non-nucleobase structures can support productive RISC interactions, offering new opportunities in the chemical engineering of therapeutic siRNAs and other classes of small-RNA drugs.","journal":"Nucleic Acids Research","year":2025,"id":587702,"datarank":0.0,"base_score":0.0,"endowment":0.0,"self_citation_contribution":0.0,"citation_network_contribution":0.0,"self_endowment_contribution":0.0,"citer_contribution":0.0,"corpus_percentile":null,"corpus_rank":null,"citation_count":0,"citer_count":0,"citers_with_citation_signal":0,"citers_with_endowment":0,"datacite_reuse_total":0,"is_dataset":false,"is_dataset_confidence":0.9551,"is_data_producer":false,"deposit_databanks":null,"is_oa":true,"file_count":0,"downloads":0,"has_version_chain":false,"published_date":"2025-01-01","fair_score":null,"fair_percentile":null,"algorithm_id":"datarank_citation_only_1hop_v6","ranking_scope":"data_only","authors":[{"id":1028147,"name":"Raymond Furgal","orcid":"0000-0002-4757-7339","position":1,"is_corresponding":false},{"id":1503776,"name":"Vella M Ross","orcid":null,"position":2,"is_corresponding":false},{"id":310200,"name":"Eric Luu","orcid":null,"position":3,"is_corresponding":false},{"id":1030862,"name":"Katherine Y. Gross","orcid":"0000-0002-3468-0345","position":4,"is_corresponding":false},{"id":302554,"name":"Vignesh Hariharan","orcid":"0000-0001-9624-1244","position":5,"is_corresponding":false},{"id":1007566,"name":"Ashley Summers","orcid":"0000-0002-5425-0457","position":6,"is_corresponding":false},{"id":38201,"name":"David Cooper","orcid":"0000-0002-4595-3943","position":7,"is_corresponding":false},{"id":1333117,"name":"Sarah Allen","orcid":"0000-0002-5776-4285","position":8,"is_corresponding":false},{"id":1459867,"name":"Christopher D Dahlke","orcid":null,"position":9,"is_corresponding":false},{"id":1503777,"name":"Mohamad Omar Rachid","orcid":null,"position":10,"is_corresponding":false},{"id":889767,"name":"Io Long Chan","orcid":null,"position":11,"is_corresponding":false},{"id":1444845,"name":"Hassan H Fakih","orcid":null,"position":12,"is_corresponding":false},{"id":398076,"name":"Julia F. Alterman","orcid":"0000-0002-6195-0857","position":13,"is_corresponding":false},{"id":173642,"name":"Dimas Echeverria","orcid":null,"position":14,"is_corresponding":false},{"id":1503778,"name":"J. Watts","orcid":null,"position":15,"is_corresponding":false},{"id":302206,"name":"Anastasia Khvorova","orcid":"0000-0001-6928-8071","position":16,"is_corresponding":false},{"id":672624,"name":"Daniel O’Reilly","orcid":"0000-0003-0012-5623","position":0,"is_corresponding":true}],"reference_count":41,"raw_metadata":null,"created_at":"2026-07-19T02:59:39.958043Z","pmid":"41521659","pmcid":null,"fwci":null,"citation_percentile":null,"influential_citations":0,"oa_status":null,"license":null,"views":0,"total_file_size_bytes":0,"version_count":0,"fair_f":null,"fair_a":null,"fair_i":null,"fair_r":null,"fair_zscore":null,"fair_rationale":null,"fair_model":null,"fair_agent_version":null,"fair_fulltext_source":null,"fair_has_llm":null,"fair_computed_at":null,"clinical_trials":[],"software_tools":[],"db_accessions":[],"linked_datasets":[],"topics":[]}