Thiophosphorylation and phosphorylation of chromatin proteins from calf thymus in vitro

Thiophosphorylation and phosphorylation of 5% perchloric acid extractable proteins from calf thymus chromatin were studied using a cyclic GMP-dependent protein kinase from bovine lung and a nuclear protein kinase II from rat liver. The phosphorylation reaction catalyzed by nuclear protein kinase II utilized [gamma -35S]ATP as a phosphate donor almost as efficiently as [gamma -32P]ATP, but the cGMP-dependent protein kinase mediated phosphorylation by [35S]ATP was about 20 times less effective than that by [32P]ATP. In addition, using [35S]ATP instead of [32P]ATP changed markedly the cGMP-dependent phosphorylation pattern of the PCA-extractable proteins as examined by gel electrophoresis. Thus, depending on the type of protein kinase, the results from thiophosphorylation and phosphorylation reactions may vary considerably.