Characterization of highly phosphorylated subcomponents of rat thymus H1 histone

The phosphorylation of electrophoretically homogeneous preparations of the five major subcomponents of that thymus H1 histone by growth-associated histone kinase isolated from Ehrlich ascites tumor or Novikoff hepatoma cell chromatin results in the introduction of three to six phosphates/molecule into different subcomponents. Fully phosphorylated preparations of subcomponents 1 through 4 consist of H1 molecules containing a uniform number of phosphate groups, and run as single bands in long acid-urea gels. Fully phosphorylated preparations of subcomponent 5 consist of a mixture of molecules containing five and six phosphate groups. Phosphorylation of subcomponents 2, 4, and 5 occurs in both the NH2- and carboxyl-terminal regions of the molecules. Phosphorylation of subcomponents 1 and 3 occurs only in the carboxyl-terminal region. The central globular region of the histones is not phosphorylated. The major sites of phosphorylation in rat H1 histone subcomponents are similar to, but not entirely identical with, the major sites of phosphorylation previously characterized in total calf thymus H1, as determined by comparison of phosphopeptide maps. Highly phosphorylated rat H1 molecules, similar in phosphate content to those found in mitotic cells, have distinct chromatographic properties, compared to lightly phosphorylated molecules of the type found in interphase cells. This change in chromatographic properties appears to depend on the number of phosphate groups present in the histone rather than on the presence of phosphate in any specific sites.