FIG. 4.

Time course of p34^cdc2 protein kinase activity of synchronized HeLa cells untreated (control) or treated with C. botulinum C2 toxin. At 6 h after release from the amethopterin block, C2 toxin (200 ng of C2II and 100 ng of C2I per ml) was added to the medium, and the cells were further incubated at 37°C. Starting at 9 h after release from the block, every 30 min control cells (■) and cells treated with C2 toxin (●) were lysed, and p34^cdc2 was immunoprecipitated and analyzed for histone H1 kinase activity.