Modulation of the nucleosome structure by histone acetylation.

A rapid procedure for the isolation of core particles from Chinese hamster ovary cells is described which permits measurements, usually at the day of their preparation. Particles of 145 +/- 5 base pairs, derived from interphase cells, will be compared with the analogue specimens from butyrate-treated cells, metaphase cells and a standard preparation from chicken erythrocytes. Butyrate cause an increase in the acetylation of histones H3 and H4, which induces alterations of the interhistone and histone-DNA interactions. Changes in the interhistone contacts, correlated to an extension of alpha-helical segments, lead to an altered accessibility of the H3 cysteine side-chains and to a different histone displacement by protamines. On the other hand, histone-DNA contacts are loosened in parts and this is particularly evident from the changes in the premelting region of a thermal-denaturation profile.