N3-kethoxal: Azide-Functionalized Probe for RNA Structure and Accessible DNA Mapping

Executive Summary. N3-kethoxal (A8793) is a synthetic, membrane-permeable nucleic acid probe that covalently labels unpaired guanine bases in RNA or single-stranded DNA (ssDNA) via its azide group, enabling downstream bioorthogonal click chemistry labeling (product page). It exhibits high solubility (≥94.6 mg/mL in DMSO) and 98% purity, making it suitable for both in vitro and in vivo nucleic acid interrogation. N3-kethoxal underpins the KAS-seq and KAS-ATAC assays, which allow for genome-wide mapping of simultaneously accessible and ssDNA-containing chromatin regions (Marinov & Greenleaf 2025). The probe's selectivity and compatibility with click chemistry have enabled new workflows for RNA secondary structure mapping, genomic accessibility profiling, and RNA-protein interaction studies (Pepbridge 2023). These properties distinguish N3-kethoxal from conventional nucleic acid labeling reagents, setting new standards for resolution and specificity.

Biological Rationale

Gene regulation in eukaryotes involves the interplay of RNA polymerases, transcription factors, and cis-regulatory elements (cREs) such as promoters and enhancers (Marinov & Greenleaf 2025). Active cREs are frequently nucleosome-depleted, resulting in accessible DNA regions and the formation of single-stranded DNA bubbles during transcription initiation and elongation. Traditional chromatin accessibility assays (e.g., ATAC-seq, DNase-seq) map open regions but do not directly resolve ssDNA. RNA secondary structure is also a key determinant of function, and mapping unpaired guanine residues provides direct information on local and higher-order RNA folding (AT7519Hydrochloride 2023). N3-kethoxal's selectivity for unpaired guanines enables high-resolution characterization of nucleic acid structure and accessibility, illuminating regulatory processes at the molecular level.

Mechanism of Action of N3-kethoxal

N3-kethoxal (3-(2-azidoethoxy)-1,1-dihydroxybutan-2-one; CAS 2382756-48-9) penetrates cell membranes and reacts specifically with the N1 and N2 positions of unpaired guanine bases in RNA and single-stranded DNA (Marinov & Greenleaf 2025). The reaction forms a stable covalent adduct, introducing an azide functional group to the nucleic acid. This azide enables subsequent labeling via copper-catalyzed or strain-promoted click chemistry (e.g., with biotin-alkyne), facilitating efficient pulldown and detection (EYFPMRNA 2023). The selectivity for unpaired guanines ensures that only regions of nucleic acid with local single-strandedness or dynamic secondary structure are tagged, supporting structural and functional readouts in both living cells and isolated nucleic acids.

Evidence & Benchmarks

• N3-kethoxal covalently labels unpaired guanine residues in ssDNA and RNA with high specificity, enabling detection of accessible genomic regions and RNA secondary structure (Marinov & Greenleaf 2025).
• The KAS-ATAC assay, powered by N3-kethoxal labeling and Tn5 transposition, maps simultaneously accessible and ssDNA-containing DNA fragments genome-wide in mammalian cells (Marinov & Greenleaf 2025).
• Quantitative solubility: N3-kethoxal dissolves at ≥94.6 mg/mL in DMSO, ≥24.6 mg/mL in water, and ≥30.4 mg/mL in ethanol under ambient conditions (ApexBio).
• 98% chemical purity is routinely confirmed by HPLC and NMR, as supplied by the manufacturer (ApexBio).
• Application in RNA structure mapping: N3-kethoxal labeling followed by click chemistry enables transcriptome-wide identification of unpaired guanine positions in living cells (Pepbridge 2023), updating prior probe-based methods.

Applications, Limits & Misconceptions

N3-kethoxal can be applied in a spectrum of nucleic acid research workflows:

• Genome-wide mapping of accessible DNA regions and ssDNA bubbles using KAS-ATAC and KAS-seq (Marinov & Greenleaf 2025).
• RNA secondary and tertiary structure probing at single-nucleotide resolution in vitro and in vivo (AT7519Hydrochloride 2023).
• Characterization of RNA-protein and RNA-RNA interaction dynamics via proximity labeling (CAS9-mRNA 2023).
• Single-molecule multiomics approaches, coupling N3-kethoxal labeling with other chromatin and transcriptome profiling modalities (Marinov & Greenleaf 2025).

Compared to earlier probes, N3-kethoxal uniquely combines membrane permeability, azide-functionalization (enabling bioorthogonal click chemistry), and high specificity for unpaired guanine. For a broader context, see Biotin-Azide 2023, which details experimental setup and troubleshooting strategies; this current article updates those recommendations with newly benchmarked in vivo protocols and KAS-ATAC-specific considerations.

Common Pitfalls or Misconceptions

• Not a universal ssDNA marker: N3-kethoxal specifically labels unpaired guanine bases, not all single-stranded regions.
• Not suited for long-term solution storage: The compound should be stored at -20°C and is unstable in solution over extended periods (ApexBio).
• Requires click-compatible downstream chemistry: Detection and pulldown steps are reliant on bioorthogonal click chemistry; improper reagent compatibility can limit assay success.
• Limited detection of double-stranded or tightly structured regions: N3-kethoxal does not react with fully base-paired guanines, so highly structured or protein-bound regions may be underrepresented.
• Not a direct reporter of transcriptional activity: While ssDNA bubbles are often associated with RNA polymerase activity, N3-kethoxal does not directly distinguish between paused, elongating, or non-transcribed ssDNA states.

Workflow Integration & Parameters

N3-kethoxal can be seamlessly integrated into both in vitro and in vivo workflows. In KAS-ATAC, cells or nuclei are incubated with N3-kethoxal (typically 1–2 mM final concentration, 37°C, 5–10 min), followed by quenching, DNA purification, and click chemistry-mediated tagging (e.g., biotinylation). Subsequent pulldown and sequencing allow for enrichment and mapping of accessible and ssDNA-containing regions (Marinov & Greenleaf 2025). For RNA structure probing, similar labeling conditions are followed, with downstream library preparation tailored to transcriptome-wide analyses. The probe's high solubility in DMSO, water, and ethanol allows for flexible stock preparation. For best practice, store N3-kethoxal as a lyophilized solid at -20°C and avoid repeated freeze-thaw cycles. Shipping conditions (blue ice or dry ice) are optimized for compound integrity (ApexBio).

Compared to EYFPMRNA 2023, which focuses on single-molecule genomic mapping, this article extends the discussion to multimodal readouts and practical integration tips for multiomics workflows.

Conclusion & Outlook

N3-kethoxal (A8793) sets a new benchmark for membrane-permeable, azide-functionalized nucleic acid probes. Its high specificity for unpaired guanine, compatibility with click chemistry, and robust performance in both RNA and DNA structure mapping underpin its adoption in cutting-edge genomics workflows. Future applications are likely to include single-molecule multiomics, integration into CRISPR specificity studies, and deeper exploration of RNA-protein interaction landscapes. For product specifications and ordering, visit the N3-kethoxal product page.