FIG. 8.
Stress regulation of Hbo1 is p53 dependent in MEFs. (A) Flow cytometry of MEF cells. MEF cell cultures from wild-type mouse embryos (top row) and p53 null embryos (bottom row) were split into three portions and either left untreated, treated with 10 mM HU for 6 h, or salt shocked with 0.24 M NaCl for 3 h. Cells were harvested, stained for DNA, and assayed by flow cytometry. The DNA content histograms are plotted as described for Fig. 7A. (B) Primary MEF cell cultures from p53+/+ and p53−/− animals were left untreated (lanes 1 and 4), stressed for 3 h with 0.24 M NaCl (lanes 2 and 5), or treated for 6 h with 10 mM HU (lanes 3 and 6). Whole-cell extracts were probed for levels of Hbo1, p53, and α-tubulin, as a loading control, by Western blot assays. Immunoprecipitates were prepared from the extracts with anti-Hbo1 antibody and assayed for HAT activity by [3H]acetate incorporation (“Fluorogram”) using chicken core histones as a substrate (“Stain”).