Influence of histones H1/H5 on the DNA coiling in the nucleosome — electric dichroism and birefringence study

Removal of histones H1 and H5 from chicken erythrocyte mononucleosomes results in a large increase of the negative electric birefringence and dichroism, and of the relaxation times, towards the values observed for mononucleosomal DNA. Cross-linking with dimethylsuberimidate does not yield important changes in the electro-optical properties of mononucleosomes, provided that the reaction is performed at low ionic strength. We suggest that in the absence of H1/H5 the linker DNA is flexible, and that this DNA tail is unwound at low ionic strength and responsible for most of the negative anisotropy of these particles. Bipolar pulse experiments revealed that the orientation mechanism of chromatosomes and H1/H5-depleted nucleosomes is predominantly of the induced dipole type.