Investigation of the sites phosphorylated in lysine-rich histones by protein kinase from pig brain

Abstract

1. Introduction The specificity of a large class of enzymes, which transfer y-phosphate of ATP to protein substrates, the so-called protein kinases (ATP: protein phosphotrans- ferases, EC 2.7.1.37), has not been investigated yet. A large number of protein kinases from different tissues has been described; these enzymes phosphory- late a wide variety of proteins like albumin, casein, ribosomal and nuclear acidic proteins, histones, etc. [l-3]. An outstanding enzyme in this respect is the pig brain cyclic-AMP-dependent protein kinase (histone kinase) which specifically phosphorylates lysine-rich histonzs only [4]. The present communication is concerned with the sites of phosphorylation of Fl, F2a2, and F2b histones by this enzyme. 2. Materials and methods Cyclic AMP was obtained from Sigma, [Y-~‘P] -ATP (0.1 Ci/mmol) from Amersham, and DNS-Cl* from Merck; the latter was twice recrystallized from benzene. Pig brain histone kinase was isolated according to the method described elsewhere [4]. Histone fractions were obtained from calf thymus as described by Jones [5]. The phosphorylation of histones by homogeneous histone kinase (0.003 mg) was run for 20 hr at 30°C