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DNA looping by the Sfi I restriction endonuclease
1Department of Biochemistry, School of Medical Sciences, Bristol, BS8 1TD, UK.
Journal of Molecular Biology
|August 12, 1998
Summary
The SfiI endonuclease forms DNA loops to cleave DNA, with loop stability varying sinusoidally with distance and enhanced by supercoiling. This study characterizes these looping interactions on different DNA forms.
Area of Science:
- Molecular Biology
- Biochemistry
- Structural Biology
Background:
- The SfiI endonuclease requires interaction with two recognition sequences to cleave DNA.
- Understanding the mechanism of DNA cleavage by multi-site interacting enzymes is crucial.
Purpose of the Study:
- To demonstrate DNA looping in SfiI endonuclease reactions.
- To characterize DNA looping interactions on supercoiled and linear DNA.
- To investigate the influence of DNA topology on SfiI-mediated looping.
Main Methods:
- Construction of plasmids with varying DNA lengths between two SfiI sites (104-211 bp).
- Testing both supercoiled and linear DNA substrates with SfiI.
- Monitoring DNA cleavage rates and partially cleaved products.
Main Results:
- SfiI-mediated DNA looping was observed on both supercoiled and linear DNA.
- Complex stability varied sinusoidally with the distance between SfiI sites, indicating helical periodicity.
- DNA supercoiling significantly stabilized the looping interaction.
- Helical repeat of approximately 11.5 base pairs per turn was determined from supercoiled DNA reactions.
Conclusions:
- SfiI endonuclease utilizes DNA looping for cleavage, dependent on the distance between recognition sites.
- DNA topology, specifically supercoiling, plays a critical role in stabilizing these looping interactions.
- The observed helical periodicity provides insights into DNA structure and enzyme-DNA interactions.