Properties of an Acidic Histone-binding Protein Fraction from Cell Nuclei

Calf thymus nuclei contain a histone-binding protein which specifically deacetylates histone Fractions F2A1 and F3 by a hydrolytic cleavage of e-N-acetyllysyl residues. The protein has been purified over 500-fold by a combination of exclusion chromatography and isoelectric focusing techniques. It is acidic, as judged by its amino acid composition, and by its isoelectric point (pH 4.5). The protein contains tryptophan and is phosphorylated. Its molecular weight is estimated at 150,000 to 160,000. Histone-binding studies show that the isolated acidic protein selectively precipitates Histones F2A1 and F3, both of which are substrates for the deacetylase activity. The isolated phosphoprotein attaches to chromatin fractions in vitro.