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Higher-order structure of mammalian chromatin deduced from viscoelastometry data
J Y Ostashevsky1, B Reichman, C S Lange
1Department of Radiation Oncology, SUNY Downstate Medical Center, Brooklyn, NY 11203, USA.
Journal of Biomolecular Structure & Dynamics
|January 15, 2000
Summary
Viscoelastometry of mammalian chromosomes revealed shorter relaxation times than expected. Applying a loop cluster model suggests chromatin fibers form loop clusters, resolving this discrepancy in DNA structure.
Area of Science:
- Molecular Biology
- Biophysics
- Genetics
Background:
- Mammalian chromosome viscoelastometry (VE) shows unexpectedly short relaxation times compared to linear DNA models.
- This discrepancy challenges current understanding of chromosome structure and DNA dynamics.
Purpose of the Study:
- To reconcile the observed VE results with established models of chromosome structure.
- To apply a specific G1 chromosome structure model involving loop clusters (micelles) to explain VE data.
Main Methods:
- Utilized viscoelastometry (VE) data from plateau phase V79 Chinese hamster cells.
- Applied a G1 chromosome structure model with parameters for loops per micelle (f) and average loop size (Mf).
- Analyzed data from both unirradiated and X-irradiated cells (up to 40 Gy).
Main Results:
- The number of loops per micelle (f) was estimated to be approximately 13, consistent with model predictions (10-20).
- The average loop size (Mf) was estimated at approximately 2 Mbp, aligning with nucleoid data (1.3 Mbp) and literature values (1-3 Mbp).
Conclusions:
- The G1 chromosome structure model, featuring a string of loop clusters, successfully explains the puzzling VE results for mammalian DNA.
- This study provides quantitative estimates for key structural parameters of chromatin fibers within chromosomes.