Modulation by exogenous histones of phosphorylation of non-histone nuclear proteins in isolated rat liver nuclei.

The phosphorylation of specific non-histone proteins in isolated rat liver nuclei is modified by the addition of exogenous histone fractions. The added histones are quantitatively adsorbed and their presence in the chromatin has been verified by electron microscope autoradiography. Histone fractions Fl and FZAl stimulate phosphorylation of different nuclear phosphoproteins. Fl stimulates the phosphorylation of a protein fraction with a molecular weight of about 40,000, while FZAl enhances phosphorylation of a protein fraction with a molecular weight of about 22,000. Fl and F2Al each inhibit the phosphorylation of a specific low molecular weight nuclear protein fraction. Histones FZAZ, FZB and F3 have little effect on the phosphorylation of non-histone proteins under these conditions. The results suggest that individual histones may be involved in the control of phosphorylation of specific non-histone nuclear proteins, particularly at times when the concentrations of nuclear proteins are changing relative to one another.