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Mobility of positioned nucleosomes on 5 S rDNA
S Pennings1, G Meersseman, E M Bradbury
1Department of Biological Chemistry, School of Medicine, University of California, Davis 95616.
Journal of Molecular Biology
|July 5, 1991
Summary
Histone octamers on sea urchin 5S rDNA exhibit dynamic positioning. Minor nucleosome positions represent fluctuations around a major site, influenced by temperature and Mg2+ ions.
Area of Science:
- Molecular Biology
- Genetics
- Biochemistry
Background:
- Nucleosome positioning is crucial for DNA regulation.
- The sea urchin 5S rDNA is a well-established model for studying nucleosome formation.
- Understanding nucleosome dynamics is key to deciphering gene expression control.
Purpose of the Study:
- To investigate the dynamic nature of nucleosome positioning on sea urchin 5S rDNA.
- To characterize the equilibrium between major and minor histone octamer binding sites.
- To determine factors influencing histone octamer mobility.
Main Methods:
- Micrococcal nuclease digestion
- DNase I footprinting
- Restriction enzyme analysis
- Two-dimensional nucleoprotein gel electrophoresis
Main Results:
- Histone octamers assemble in a dominant position with minor positions nearby on 5S rDNA.
- These positions are in dynamic equilibrium under low ionic conditions.
- Octamer mobility is dependent on temperature and reversibly inhibited by Mg2+ ions.
Conclusions:
- Nucleosome positioning on 5S rDNA is not static but dynamic.
- Minor positions reflect transient fluctuations around the primary binding site.
- Environmental factors like temperature and ion concentration modulate nucleosome dynamics.