[Optical and hydrodynamic properties of DNA complexes with histones H1 from the calf thymus and sea urchin sperm]

A comparative study of the complexes between DNA and H1 histones from calf thymus (H1-T) and sea urchin sperm (H1-S) has been performed using methods of flow birefringence, viscometry and circular dichroism (CD). Both nucleohistone complexes undergo a conformational transition with the increase of protein content. A two-fold drop of intrinsic viscosity was observed when the histone content in the complex increased up to 9-12%. The transition is not accompanied by essential changes in the nucleohistone anisotropy, the latter coincides with the anisotropy of DNA in H1-T containing complexes and is close to that in H1-S containing complexes. CD spectra of the two types of complexes are not the same. For the H1-S containing complexes the decrease of the amplitude of the CD positive band and the shift of its maximum to the longwave region are observed while the spectrum of H1-T containing complex coincides with that of DNA. The spectral changes are partly due to slight aggregation of the H1-S containing complexes. It is also possible that changes in the local structure of DNA within the H1-S containing nucleohistone complexes take place.