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bioRxiv · 10.1101/2025.11.02.686076

Dangling Ends of Third Strand and Duplex Drive Nucleic Acid Triplex Stabilization through Bimodal Association

Zhou, F.·Liu, Y.·Shu, Z.·Wang, Y.·Chen, G.
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Abstract

Nucleic acid triplexes are crucial structural motifs in gene regulation and biotechnology, yet the kinetic principles governing their formation remain poorly understood. While a stability hierarchy of RNA*DNA-DNA > DNA*DNA-DNA > RNA*RNA-RNA, with no DNA*RNA-RNA triplex forming, is known, the kinetic roles of terminal residues remain poorly understood. Here, we employ bio-layer interferometry (BLI) and circular dichroism (CD) spectroscopy to demonstrate that dangling ends from both the third strand (triplex-forming oligonucleotide, TFO) and the duplex dramatically enhance triplex stability. Kinetic analysis reveals this stabilization is primarily driven by a marked increase in the association rate (k{square}{square}). Crucially, creating a single-base-pair dangling end at either terminus of the duplex enhanced triplex stability more effectively than blunt ends. For example, DNA TFO dTFO5 binding to d(HP5+TA) was enhanced compared to dHP5, and similarly RNA TFO rTFO5 binding to RNA duplex r(HP5+UA) and DNA duplex d(HP5+TA) showed stronger affinity and faster association than to blunt-ended rHP5 and dHP5. Interestingly, removal of a terminal base pair from the blunt-end duplex, generating a TFO dangling end, also enhances binding affinity and association rate. This indicates that both duplex and TFO dangling ends provide critical nucleation platforms, while blunt-ended terminal triples are dynamic and contribute minimally to stability. Thus, our work establishes that optimal triplex formation requires strategic optimization of both TFO and duplex terminal structures through a fundamental kinetic principle (bimodal nucleation). Graphical abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=118 SRC="FIGDIR/small/686076v1_ufig1.gif" ALT="Figure 1"> View larger version (24K): org.highwire.dtl.DTLVardef@1dc6950org.highwire.dtl.DTLVardef@1861387org.highwire.dtl.DTLVardef@16c24a5org.highwire.dtl.DTLVardef@da0bf0_HPS_FORMAT_FIGEXP M_FIG C_FIG HighlightsO_LIDangling ends at both third strand and duplex termini enhance triplex stability by accelerating association C_LIO_LITriplex formation can be nucleated from either end with a bimodal association mechanism C_LIO_LITerminal blunt-end base triples are dynamic and contribute minimally to stability compared to tailored overhangs C_LI

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Zhou, F., Liu, Y., Shu, Z., Wang, Y., Chen, G.. 2025-11-03. Dangling Ends of Third Strand and Duplex Drive Nucleic Acid Triplex Stabilization through Bimodal Association. https://doi.org/10.1101/2025.11.02.686076

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