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.