Histone interactions in solution and susceptibility to denaturation

Abstract
Histone interactions in solution may depend upon treatments used for purification. Optical rotatory dispersion and sedimentation-velocity measurements were made in a reference solvent, before and after exposure to various treatments, to investigate [calf thymus] histone susceptibility to irreversible denaturation. Some acid conditions and urea and guanidine solutions may denature. Interaction studies performed on nondenatured histones indicate that the dimer, (H4)(H3), and tetramer, (H4)2(H3)2, dissociate to monomers at low ionic strength. Sedimentation-velocity experiments suggest a model for the (H4)2(H3)2 tetramer, with a compact semispherical center and 4 protruding amino-terminal regions. Fractions H2a and H2b interact to form the mixed dimer in equilibrium with monomers. Fraction H2a self-associates readily to dimers, tetramers, and octamers, while fraction H1 associates only weakly to form dimers.

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