Conformational effects of organic solvents on histone complexes

Abstract

Changes in the conformations of H3-H4, H2A-H2B and the core histone complex [from chicken erythrocyte nuclei] brought about by the addition of organic solvents were examined by circular dichroism spectroscopy. All 3 complexes assume increased .alpha. helicity with increasing amounts of the organic solvent. An amount of secondary structure equal to that obtained in phosphate-buffered 2 M NaCl solution can be induced in low-salt solutions of the complexes by the addition of 40-50% ethylene glycol, 50% glycerol, or .apprx. 2% hexafluoro-2-propanol. H3-H4 was somewhat more flexible than H2A-H2B in its response to changes in solvent polarity. Upon being heated, H3-H4 and the core histone complex both undergo irreversible .alpha. .fwdarw. .beta. transitions in 50% ethylene glycol under low-salt conditions, while H2A-H2B undergoes an essentially reversible .alpha. .fwdarw. random-coil transition under the same conditions. These results are discussed in terms of the dynamics of the nucleosome particle.