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European Biophysics Journal

, Volume 17, Issue 5, pp 245–255 | Cite as

The superstructure of chromatin and its condensation mechanism

VI. Electric dichroism and model calculations
  • M. H. J. Koch
  • Z. Sayers
  • A. M. Michon
  • P. Sicre
  • R. Marquet
  • C. Houssier
Article

Abstract

Electric dichroism and X-ray scattering measurements on solutions of uncondensed and condensed chicken erythrocyte chromatin were interpreted on the basis of model calculations. Information about the state of uncondensed fibers in the conditions of electric dichroism measurements was obtained from scattering patterns recorded as a function of pH, in the presence of spermine and at very low monovalent cation concentrations. Electric dichroism measurements on a complex of uncondensed chromatin with methylene blue were made to determine the contribution of the linker and of the nucleosomes to the total dichroism.

A new approach to calculate the dichroism from realistic structural models, which also yields other structural parameters (radius of gyration, radius of gyration of the cross-section, mass per unit length) was used. Only a restricted range of structures is simultaneously compatible with all experimental results. Further, it is shown that previous interpretations of dichroism measurements on chromatin were in contradiction with X-ray scattering data and failed to take into account the distribution of orientation of the nucleosomes in the fibers. When this is done, it is found that the linker DNA in chicken erythrocyte and sea urchin chromatin must run nearly perpendicularly to the fibre axis. Taken together with the dependence of the fibre diameter on the linker length, these results provede the strongest evidence hitherto available for a model in which the linker crosses the central part of the fibre.

Key words

X-ray solution scattering synchrotron radiation electric dichroism chicken erythrocyte chromatin 

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Copyright information

© Springer-Verlag 1989

Authors and Affiliations

  • M. H. J. Koch
    • 1
  • Z. Sayers
    • 1
  • A. M. Michon
    • 1
  • P. Sicre
    • 1
  • R. Marquet
    • 2
  • C. Houssier
    • 2
  1. 1.European Molecular Biology Laboratory, c/o DESYHamburg 52Federal Republic of Germany
  2. 2.Laboratoire de Chimie Macromoléculaire et Chimie Physique, Sart tilman (B6)Université de LiègeLiègeBelgium

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