Studies on histone acetyltransferase. Partial purification and basic properties.

A rapid and reproducible method for the purification of rat liver histone acetyltransferase is presented. Extraction of nuclei in low salt, followed by phenyl-Sepharose hydrophobic affinity chromatography, G-200 gel filtration in the presence of 1 M urea, CM-cellulose ion exchange and acetyllysine affinity chromatography minimize exposure of the enzyme to high salt. Evidence is provided which indicates that the instability of the enzyme activity is due in part to hydrophobic interactions. The molecular weight of the enzyme is 96,000 as judged by gel filtration. In agreement with others, the enzyme is unstable in the presence of divalent cations, although a requirement for low concentration of Mg2+ or Ca2+ was observed. The enzyme is also sensitive to sulfhydryl blocking agents and is susceptible to rapid thermal denaturation at 37 and 45 degrees C (t1/2 = 22.2 and 9.54 min, respectively). The optimum pH and the energy of activation for the reaction were pH 7.5 and 5230 +/- 378 cal/mol, respectively. In the presence of all five histones, the enzyme catalyzes the acetylation in the order of H3 greater than H4 greater than H2b greater than H2a greater than H1 and appears to operate in a nonprocessive manner. While no other isozymic forms of nuclear acetyltransferase were detected, the enzyme exhibits the properties of both nuclear isozymic forms which have been reported, histone acetyltransferase A and DB, observed in calf thymus and bovine lymphocytes, respectively.