Hypothetical model for cell cycle-dependent histone H1.5 serine phosphorylation in T cells and Jurkat cells. The main kinase activity takes place during late G1 and early S phase as indicated by the red segment. The relative phosphorylation level, shown as the fraction of phosphorylated H1.5 serines per DNA unit, is indicated by the width of the grey segment. For clarity, the threonine phosphorylation taking place during mitosis is shown as a widening of the grey segment at the end of the cell cycle. The obtained results on H1.5 phosphorylation fit with, but do not prove, this model.