Studies on the Role and Mode of Operation of the Very‐Lysine‐Rich Histones in Eukaryote Chromatin

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Abstract
PMR and other measurements were carried out in order to study the behavior of the lysine-rich histones .phi.1 in the sperm chromatin of certain marine invertebrates [Arbacia lixula, Paracentrotus lividus, Holothuria tubulosa, Mytilus edulis]. Well defined particles (12 S) were obtained from this chromatin by nuclease treatment. Chromatin solubility as a function of ionic strength showed a relaxation at salt concentrations higher than in the case of calf thymus nucleoprotein. NMR studies showed that the release of histone from DNA occurs both in chromatin and in the reconstituted complexes at practically the same ionic strength as solubility relaxation. The higher the arginine content of a given .phi.1, the higher the ionic strength at which both effects take place. The NMR results demonstrate that arginine residues are bound more strongly than lysine residues. The .phi.1 histones play a role in the contraction mechanism of sperm chromatin similar to that of H1 histone in calf thymus chromatin. The highly contracted state of sperm chromatin is directly related to the increased arginine content of the .phi.1 histone.