Cross-Linker Chemistry

Cross-Linking Base Modified Oligonucleotides

Custom cross-linker oligonucleotides—psoralen intercalators and halogenated bases—engineered for UV-induced covalent bonding in DNA/RNA. Designed to probe nucleic acid secondary structures and stabilize protein–nucleic acid complexes.

Overview

UV-activated cross-linking chemistries enable covalent bonds between DNA/RNA strands or between nucleic acids and proteins. These modifications are essential for structural biology, probing nucleic acid secondary structures, and mapping protein–nucleic acid interactions.

Cross-linkers fall into two categories: nucleic acid intercalators such as psoralen for site-specific targeting in double- and triple-stranded DNA, and halogenated bases like 5-bromo-dC for intra-strand or protein-directed cross-linking.

Bio-Synthesis provides custom cross-linker oligonucleotides tailored for research, diagnostics, and therapeutic applications, with scalable synthesis and full QC support.

Cross-Linking Products

Representative cross-linker modifications available for custom synthesis.

Product/Modification Description Typical Use Notes / Code
5-Bromo-dC (5-Br-dC) Halogenated cytosine analog UV-induced DNA cross-linking [5-Br-dC]
5-Iodo-dC (5-I-dC) Iodinated cytosine analog Site-specific DNA damage & protein-binding studies [5-I-dC]
5-Iodo-dU (5-I-dU) Iodinated uracil analog Cross-linking in dsDNA and protein complexes [5-I-dU]
Convertible dG Reactive guanosine analog Protein–DNA conjugation studies [Conv-dG]
Psoralen C6 Classic intercalator cross-linker Site-specific interstrand DNA cross-linking [Pso-C6]
Psoralen-TEG Psoralen with flexible linker Duplex intercalation with extended reach [Pso-TEG]
Technical Notes
  • Mechanism: UVA (≈320–365 nm) irradiation induces covalent bonds at the incorporated cross-linker site.
  • Intercalators: Psoralen inserts between bases to form site-specific links in ds/triplex DNA; placement in helical regions is key.
  • Halogenated bases: 5-Br-dC / 5-I-dC / 5-I-dU provide reactive handles for intra-strand links or direct coupling to proteins.
  • Use cases: Secondary structure probing, mapping protein–DNA contacts, photochemical assays, and crystallographic phasing aids.
  • Compatibility: Can be combined with dyes, affinity tags, and linkers; confirm purification strategy (HPLC/PAGE) based on construct.

Design & Strategy

Placement & Architecture

  • Intercalator targeting: Place psoralen within stable ds/triplex segments (preferably GC-rich neighborhoods) for efficient cross-linking.
  • Intra-strand goals: Choose halogenated bases when the objective is an intra-strand link or direct protein capture.
  • Spacing & reach: Flexible spacers (e.g., TEG) can improve accessibility to the intended partner strand or protein.
  • Context mixing: Cross-linkers can be blended with 2′-OMe/MOE/LNA wings or PS backbones to tune stability and PK.
  • Probe vs. therapeutic: For analytical probes, prioritize signal and specificity; for therapeutics, emphasize safety and clearance.

We can model Tm and suggest positions to balance cross-link yield with hybridization and off-target risk.

UV Exposure & Controls

  • Wavelength: UVA (≈320–365 nm) is typical for psoralen activation; verify lamp spectrum and dose in your buffer.
  • Dose titration: Run brief time courses to optimize yield while minimizing non-specific photochemistry.
  • Controls: Include “no-UV” and “no-modifier” controls to confirm cross-linker dependence.
  • Analysis: Validate by denaturing PAGE/HPLC and MS where applicable; map sites with primer extension or digest-MS workflows.

We can provide small-scale pilot lots for method optimization prior to scale-up.

Chemistry & QC

Chemistry

  • Intercalators: Psoralen C6, Psoralen-TEG (other linkers on request).
  • Halogenated bases: 5-Br-dC, 5-I-dC, 5-I-dU; convertible dG for protein capture.
  • Backbones: PO, PS, and mixed; conjugations (dyes, affinity tags, peptides, PEG, chelators) supported.

Purification via HPLC/PAGE per construct; conjugates may use RP-HPLC with diafiltration.

QC & Documentation

  • Identity by ESI-MS/MALDI; purity by HPLC; optional SEC for conjugates.
  • COA includes yield (OD/µmol), method parameters, and impurity profile.
  • ISO 9001 / ISO 13485 alignment; GLP/GMP-like practices as scoped.

We can align to internal SKUs and report extinction coefficients for modified bases.

Need help selecting the right cross-linking base?

Our team can recommend optimal modification sites, UV conditions, and QC strategies for your project.

FAQ

When should I use psoralen vs. halogenated bases?

Psoralen intercalators are preferred for site-specific interstrand links in double- or triple-helical regions. Halogenated bases (e.g., 5-Br-dC, 5-I-dU) are often chosen for intra-strand links or direct protein capture.

Can cross-linkers be combined with dyes or affinity tags?

Yes. Cross-linkers are compatible with a wide range of conjugations; we’ll advise on placement and purification to avoid interference.

Do cross-linker bases affect duplex stability?

Effects are context-dependent; we recommend verifying Tm in your buffer and adjusting length or adding stabilizing sugars (2′-OMe/MOE/LNA) as needed.

Speak to a Scientist

Tell us about your cross-linker oligo project

Please avoid confidential details; we can arrange an NDA if needed.

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