396: Physical homology recognition between DNA duplexes

Stannard A et al., Proceedings of the National Academy of Sciences (PNAS) - This episode summarizes a PNAS study that uses a FRET-responsive DNA tweezers nanosensor to detect and quantify sequence-dependent interactions between intact double-stranded DNA duplexes in ionic solutions. Key terms: homologous recognition, double-stranded DNA, electrostatic interactions, DNA nanosensor, divalent cations. Study Highlights:Using a tuned DNA-tweezers FRET assay, the authors show that homologous dsDNA duplexes coalign more readily than heterologous ones in the presence of divalent cations. They quantify a homologous recognition free energy of roughly −0.02 kBT (≈ −0.01 kcal/mol) per base pair and show this is largely independent of Mg2+ versus Ca2+ within the tested range. Controls exclude strand exchange and sequence-specific ion adsorption as alternative explanations. An electrostatic helical coherence model reproduces the magnitude and salt dependence of the measured effect. Conclusion:Protein-free, sequence-specific electrostatic interactions between intact dsDNA can produce a small but measurable homology recognition energy consistent with helical coherence theory and relevant under confined, DNA-rich conditions. Music:Enjoy the music based on this article at the end of the episode. Article title:Direct evidence and quantification of homologous recognition between DNA duplexes First author:Stannard A Journal:Proceedings of the National Academy of Sciences (PNAS) DOI:10.1073/pnas.2530949123 Reference:Stannard A., Haimov E., Hedley J.G., et al. Direct evidence and quantification of homologous recognition between DNA duplexes. Proc. Natl. Acad. Sci. U.S.A. 2026; doi:10.1073/pnas.2530949123. License:This episode is based on an open-access article published under the Creative Commons Attribution 4.0 International License (CC BY 4.0) – https://creativecommons.org/licenses/by/4.0/ Support:Base by Base – Stripe donations: https://donate.stripe.com/7sY4gz71B2sN3RWac5gEg00 Official website https://basebybase.com On PaperCast Base by Base you'll discover the latest in genomics, functional genomics, structural genomics, and proteomics. Episode link: https://basebybase.com/episodes/homologous-dna-recognition-396 QC:This episode was checked against the original article PDF and publication metadata for the episode release published on 2026-06-18. QC Scope:- article metadata and core scientific claims from the narration- excludes analogies, intro/outro, and music- transcript coverage: Audited the transcript portions describing the DNA tweezers design and readout, cation dependence, homologous vs heterologous comparison, longer-duplex effects, strand-exchange controls, helical-coherence theory, and cellular relevance.- transcript topics: DNA tweezers design and FRET readout; Monovalent vs divalent cation effects on duplex coalignment; Homologous versus heterologous sequence comparisons; Strand-exchange controls and GC clamps; Length dependence: 36 bp vs 68 bp and entropic effects; Helical coherence theory mechanism and charge patterning QC Summary:- factual score: 10/10- metadata score: 10/10- supported core claims: 7- claims flagged for review: 0- metadata checks passed: 4- metadata issues found: 0 Metadata Audited:- article_doi- article_title- article_journal- license Factual Items Audited:- Direct evidence for homologous recognition between intact dsDNA in protein-free ionic conditions.- Recognition energy per base pair is about -0.02 kBT (≈ -0.01 kcal/mol per base pair).- Recognition is largely independent of whether Mg2+ or Ca2+ is the divalent cation and of their concentration within tested range.- Divalent cations promote coalignme...