FIG. 1.

The activity of two H3 kinases of 50 and 45 kDa correlates with histone H3 mitotic phosphorylation. HeLa cells were synchronized by a double thymidine block and harvested at 0, 3, 5, 7, 10, and 12 h after being released from the block. Progression through the cell cycle and the consequent accumulation of phosphorylated histone H3 was verified by Western blotting using the anti-phosphorylated histone H3 antibody (anti-P.H3). Protein extracts (10 μg) (total extract and 600 mM soluble fractions), prepared at the indicated times, were analyzed by an in-gel kinase assay, using histone H3 (top) or BSA (bottom) as substrates. Equal loading was checked by Coomassie staining.