Relevance of histone H1 kinase activity to the G2/M transition during the cell cycle ofDictyostelium discoideum.

The implication of histone H1 kinase activity for the G2/M transition during the cell cycle was investigated usingDictyostelium discoideum Ax-2. Histone H1 kinase with its activity was purified from cell extracts by the use of p13(suc1) affinity gel. In the vegetative cell cycle, the activity of histone H1 kinase including Cdc2 kinase was found using synchronized Ax-2 cells to be highest just before the entry into mitosis. The activity also was markedly enhanced just prior to the M phase from which developing cells (possibly prespore cells) reinitiate their cell cycle at the mound-tipped aggregate stage. These results strongly suggest the importance of Cdc2 kinase activity in the G2 to M phase transition during the cell cycle, as the case for other eukaryotic cells.