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Single-Molecule Fluorescence Visualization of DNA Polymerase Dynamics at G-Quadruplexes
Published on: April 4, 2025
Unique dynamic properties of DNA duplexes containing interstrand cross-links
Joshua I Friedman1, Yu Lin Jiang, Paul S Miller
1Department of Pharmacology and Molecular Sciences, Johns Hopkins University School of Medicine, WBSB 314, 725 North Wolfe Street, Baltimore, Maryland 21205, United States.
Biochemistry
|December 23, 2010
Summary
DNA interstrand cross-links (ICLs) are potent cytotoxins repaired by recognizing common damage features. This study synthesized homogeneous ICL DNAs to investigate structural dynamics, finding intrinsic DNA dynamics are not required for repair, but an immobile Y-junction is essential.
Area of Science:
- Molecular Biology
- DNA Repair Mechanisms
- Chemical Biology
Background:
- Bifunctional DNA alkylating agents create DNA interstrand cross-links (ICLs), which are cytotoxic.
- Cellular recognition of ICLs likely relies on common damage features rather than specific cross-linker structures.
- Investigating ICL structural and dynamic properties has been challenging due to heterogeneous DNA incorporation.
Purpose of the Study:
- To synthesize and characterize homogeneous ICL DNAs with site-specific staggered cross-links.
- To understand how structural and dynamic properties of diverse ICLs flag sites for DNA repair.
- To determine the role of intrinsic DNA dynamics in the incision of ICLs.
Main Methods:
- Synthesis of homogeneous ICL DNAs with site-specific staggered N4-cytosine-ethyl-N4-cytosine cross-links.
- Introduction of cross-links in ways that preserve B-form DNA or highly distort DNA structure.
- Measurement of base pair opening dynamics using (1)H NMR line width and imino proton solvent exchange.
- Incubation of ICL-containing DNA duplexes in mammalian whole cell extracts.
Main Results:
- B-form ICL duplexes showed significantly slower guanine base pair opening dynamics compared to controls.
- B-form ICLs reduced base pair opening dynamics extending to adjacent base pairs.
- Non-B-form ICLs exhibited extensive conformational dynamics across the entire DNA sequence.
- Both B-form and non-B-form ICL duplexes were incised in cell extracts, unlike normal duplex DNA.
Conclusions:
- Intrinsic DNA dynamics are not a prerequisite for the specific incision of ICL damage.
- Destabilized ICL duplexes may energetically facilitate the binding of DNA repair factors.
- An immobile Y-junction, where repair factors bind stably to unpaired DNA strands, is essential for ICL incision.
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