Purification and Properties of a Histone Acetyltransferase from Artemia salina, Highly Efficient with H1 Histone

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Abstract
A histone acetyltransferase [EC 2.3.1.48] was purified from nuclei of 40 h old A. salina larvae. The enzyme is very unstable at 0.degree. C, requires free -SH groups for activity and is rapidly inactivated at 40.degree. C. The optimal pH for activity is 8.5 and the activity is half inhibited by millimolar concentrations of Mn2+, Ca2+ or Mg2+ or decimolar concentrations of Na+ and K+. The molecular weight of the enzyme, determined by gel filtration chromatography, changed with the ionic strength of the medium (280,000 in 10 mM Tris .cntdot. HCl, 170,000 in 0.2 M KCl). The very lysine-rich histone H1 is a better substrate acceptor than the arginine-rich histones H3 or H4, Under proper conditions, the enzyme can modify all the internal lysyl residues in histones H1 and H4. The acetylation of H1 is inhibited when all the other histone fractions are present in the assay mixture.