FIG. 2.

The only major Orc1-associated protein kinase activity appears during mitosis. Metaphase cells were collected either in the absence (shake-off) or in the presence of nocodazole and then released into G₁ phase (post-noc) for the times indicated. Total ORC proteins were extracted and then immunoprecipitated with either anti-Orc1 (Orc1-IP), anti-Orc2 (Orc2-IP), or normal rabbit IgG (IgG-IP). IPs were assayed for protein kinase activity by labeling histone H1 with [γ-³²P]ATP.