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Exploring rare conformational species and ionic effects in DNA Holliday junctions using single-molecule spectroscopy
Chirlmin Joo1, Sean A McKinney, David M J Lilley
1Physics Department, University of Illinois, Urbana-Champaign, Urbana, IL 61801, USA.
Journal of Molecular Biology
|August 4, 2004
Summary
The study reveals that the DNA (Holliday) junction frequently adopts an open conformation, crucial for DNA recombination. Parallel conformations are extremely rare, suggesting the open form is key for protein interactions.
Area of Science:
- Molecular Biology
- Biophysics
- Structural Biology
Background:
- The four-way DNA (Holliday) junction is a critical intermediate in DNA recombination.
- Its dynamic structural transitions are vital for cellular processing.
Purpose of the Study:
- To investigate rare structural conformations of the DNA (Holliday) junction, specifically open and parallel forms.
- To further characterize the influence of ionic environments on junction dynamics.
Main Methods:
- Single-molecule fluorescence spectroscopy was employed to observe conformational transitions.
- Investigated the effects of varying magnesium, sodium, and hexammine cobalt (III) ion concentrations.
Main Results:
- The DNA (Holliday) junction frequently transitions to an open conformation, hundreds of times per second under physiological conditions.
- Parallel conformations were not detected, with a probability of less than 0.01% for lifetimes exceeding 5 ms.
- Ion concentration and valence affect transition rates, with lower valence ions showing higher rates.
Conclusions:
- The frequently formed, though transient, open conformation is likely stabilized by protein binding during DNA recombination.
- Electrostatic interactions play a significant role in stabilizing stacked DNA junction structures and influencing interconversion rates.