Physical studies on the H3/H4 histone tetramer

Abstract

High-resolution PMR spectroscopy (270 MHz), circular dichroism and IR spectroscopies and ultracentrifugation studies were carried out on the salt-extracted (H3/H4)2 tetramer from calf thymus. The tetramer contains about 29% .alpha. helix and no .beta. structure. It is denatured in 6 M urea but can be renatured simply by dialysis to water. The proton spectrum shows a number of perturbed resonances which are not observed in the spectra of either H3 or H4 alone. Some elements of tertiary structure were demonstrated in the tetramer by these resonances. The overall appearance of the spectrum is close to a partially denatured protein. Sedimentation velocity studies show the tetramer to have a frictional ratio of 1.99 in 50 mM acetate/50 mM bisulfite and thus to be hydrodynamically quite different from a globular protein. Two possible structural models compatible with the data are discussed.