Spermine-induced phosphorylation of myotube histones by endogenous nuclear protein kinases

The effects of spermine on phosphorylation of nuclear proteins in isolated nuclei from proliferation and myotube stage cells during differentiation of cultured chicken myoblasts have been investigated. Incorporation of phosphate from 32P-gamma-ATP was assessed by incubating nuclei with and without 2 mM spermine, which caused an approx. 1.5-fold increase in phosphorylation of total nuclear proteins in both cell types. Modification of individual proteins was assessed by extracting basic proteins in dilute acid, followed by SDS-electrophoresis on 18% acrylamide gels and radioautography. Results indicated that whereas most phosphoproteins in both cell types were increased 1.5-2.0-fold, phosphorylation of a 31 000 D band increased several-fold. Most strikingly, myotube nuclei displayed selective 3.5- and 9-fold increases in specific radioactivity of histones Hla and H3, respectively, which normally exhibit little, if any, phosphorylation.