PKC isoforms phosphorylate human recombinant DNMT1. (A) Quantitative measurements of phosphorylation of 5 nM of DNMT1 in the presence of (γ-32P)ATP for 30 minutes at 30°C with the indicated amounts of activated recombinant human PKCα, δ, ε, μ or ζ. DNMT1 phosphorylation was quantified as the ratio of PKC activity to negative control. Data represent the average of two representative independent experiments. Bars, S.D. (B) PKC activity of recombinant PKC isoforms against CREB, showing that all isoforms were active. 20 nM of each PKC and 1.5 μM of CREB peptides were used for the assay and were incubated in the presence of (γ-32P)ATP for 30 minutes at 30°C. Bars, S.D. (C) Autoradiography of a SDS-PAGE showing incorporation (γ-32P)ATP in recombinant human DNMT1 following incubation with different amounts of human PKCζ.