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Related Experiment Videos

Solution structural studies of chromatin fibers

K S Lee, M Mandelkern, D M Crothers

    Biochemistry
    |March 17, 1981
    PubMed
    Summary

    Structural studies reveal the 30-nanometer (nm) chromatin fiber has a diameter of 33 nm and a length of 1.5 nm per nucleosome. This research provides insights into chromatin fiber structure and DNA packaging.

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    Area of Science:

    • Molecular Biology
    • Biophysics
    • Structural Biology

    Background:

    • The 30-nm chromatin fiber is a key structure for DNA packaging in eukaryotic cells.
    • Understanding its precise three-dimensional structure is crucial for comprehending gene regulation and nuclear organization.

    Purpose of the Study:

    • To investigate the solution structure of 30-nm chromatin fiber fragments.
    • To determine key structural parameters like fiber diameter, nucleosome spacing, and superhelix geometry.
    • To test proposed models for the 30-nm fiber's detailed architecture.

    Main Methods:

    • Isolation and cross-linking of 9-16 kilobase (kb) chromatin fiber fragments from calf thymus nuclei.
    • Size fractionation using sucrose gradient sedimentation.
    • Characterization via electron microscopy, sedimentation diffusion, light scattering, and gel electrophoresis.
    • Determination of frictional coefficients using quasielastic light scattering and transient electric dichroism.

    Main Results:

    • The 30-nm chromatin fiber exhibits a diameter of 33 ± 3 nm and a length of 1.5 ± 0.1 nm per nucleosome.
    • Calculated nucleosome density is 7.5 ± 0.5 nucleosomes per superhelical turn, assuming an 11 nm pitch.
    • The fiber lacks polarity and shows an average angle of 51 degrees between the fiber axis and the nucleosomal superhelix axis, ruling out simple structural models.

    Conclusions:

    • The study provides quantitative structural data for the 30-nm chromatin fiber.
    • The determined parameters refine our understanding of higher-order DNA organization.
    • Results challenge and constrain existing models for the 30-nm fiber's detailed conformation.

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