FIG. 6.
Cell death-associated histone H1 kinase activities represent cyclin A-dependent Cdks. (A) Death kinase activity was analyzed by immunodepletion analysis. Nuclear extracts from untreated DO11.10 cells or cells treated for 12 h with 10−6 M dexamethasone were analyzed for histone kinase activity following depletion with antibody specific for the indicated cyclin (αcyc) or Cdk (αCdk 2) or with irrelevant anti-Myc (αMyc) antibody. (B) Nuclear extracts from DE cells incubated at the restrictive temperature for 6 h and from DO11.10 cells treated with dexamethasone (Dex.) as above, as well as viable control (Ctrl.) cells, were treated with p9cksHs2 agarose to adsorb nuclear Cdk activity. Adsorbed and unadsorbed Cdk activities from 1 μg of nuclear extract were quantified. Note that for the experiments in panel A, H1 substrate peptide was used, while the activity in panel B was assayed with biotinylated H1. Comparison of DO11.10 activity in the two panels demonstrates the difference in apparent specific activity obtained with the different substrates.