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Continuous assays for DNA translocation using fluorescent triplex dissociation: application to type I restriction
Sarah E McClelland1, David T F Dryden, Mark D Szczelkun
1DNA-Protein Interactions Group, Department of Biochemistry, University of Bristol, Bristol BS8 1TD, UK.
Journal of Molecular Biology
|April 22, 2005
Summary
New fluorescent assays track DNA translocation by restriction enzymes independent of DNA unwinding. This method reveals enzyme motion and initiation kinetics, showing DNA cleavage is not required for translocation.
Area of Science:
- Biochemistry
- Molecular Biology
- Enzymology
Background:
- Type IA, IB, and IC restriction endonucleases are ATP-dependent motor proteins that translocate along DNA.
- Understanding the mechanism of DNA translocation is crucial for elucidating enzyme function and regulation.
Purpose of the Study:
- To develop novel fluorescent assays for analyzing DNA translocation independent of DNA unwinding.
- To characterize the kinetics of DNA translocation and initiation for type IA, IB, and IC restriction enzymes.
- To investigate the role of DNA cleavage in the initiation and translocation process.
Main Methods:
- Introduction of a triplex binding site (TBS) into DNA substrates downstream of endonuclease recognition sequences.
- Pre-binding of fluorescently labeled triplex-forming oligonucleotides (TFOs) to the TBS.
- Monitoring displacement of TFOs using fluorescence intensity or anisotropy changes upon ATP addition.
- Utilizing stopped-flow fluorimetry for continuous kinetic profiling.
Main Results:
- Developed assays measuring DNA translocation via TFO displacement, independent of duplex unwinding.
- Obtained kinetic profiles revealing translocation rates and initiation kinetics, including lag-phases proportional to translocation distance.
- Demonstrated that enzymes with ATPase activity but deficient in DNA cleavage exhibit identical initiation and translocation rates to wild-type enzymes.
Conclusions:
- DNA strand breaks are not a prerequisite for the initiation or translocation of these restriction enzymes.
- The developed fluorescent assays provide a robust method for studying DNA translocation mechanisms.
- Kinetic analysis revealed insights into the initiation steps and translocation rates of type IA, IB, and IC restriction enzymes.