Participation of core histone "tails" in the stabilization of the chromatin solenoid.

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Abstract
The solenoid is maintained by the combination of linker histones and the nonglobular, highly basic tails of the core histone, which play only a minor part in the formation of the nucleosome core. Polynucleosomes that contain core histones devoid of tails remain substantially unfolded under conditions otherwise favorable for the formation of solenoids. The tails can be replaced by extraneous basic polypeptides and in the presence of the linker histones the solenoid structure is then spontaneously recovered, as judged by a wide variety of structural criteria. The core histone tail segments apparently function by providing electrostatic shielding of the DNA charge and at the same time bridging adjacent nucleosomes in the solenoid. Posttranscriptional modifications, such as acetylation of .epsilon.-amino groups, that reduce the positive charge of the core histone tails may tend to destabilize the higher-order structure and could thus render the DNA with which they are associated more readily available for transcription.