Characterization of the histone core complex.

Abstract

A stable histone core complex containing equimolar ratios of H2A, H2B, H3 and H4 was isolated from chicken erythrocyte chromatin in high salt. This complex was characterized by sedimentation and chemical crosslinking studies. In velocity ultracentrifugation, only 1 single sharp sedimentation boundary was observed with sedimentation coefficient .**GRAPHIC**. = 3.8 .+-. 0.1. The MW of the histone core complex was investigated by low-speed sedimentation equilibrium studies over a wide range of protein concentration. Analysis of the apparent weight-average MW as a function of concentration indicates that the histone core complex in 2 M NaCl, pH 9.0, is in equilibrium between a tetramer (H2A)(H2B)(H3)(H4) and an octamer [(H2A)(H2B)(H3)(H4)]2 species with a tetramer MW of 55,000. The equilibrium constant K is approximately 1.2 .times. 10-5 l/mol at 10.degree. C. Evidence of such a tetramer-octamer equilibrium in solution is also supported by the results of the chemical crosslinking experiments on the histone core complex.