FIG. 4.

cHSF1-deficient cells are highly sensitive to high temperatures. (A) Wild-type DT40 (wt), double-null (54 cells), HSF1-null (59 cells), and HSF3-null (21 cells) cells were incubated at 43°C for 24 h. Representative cell cycle distributions of the indicated cell cultures are shown. Cells were pulse labeled for 10 min and stained with fluorescein isothiocyanate-conjugated antibromodeoxyuridine to detect bromodeoxyuridine incorporation (vertical axis) and propidium iodide to detect total DNA (horizontal axis). (B) Western blot analysis of HSF1 protein in cells of each indicated genotype as well as HSF1-null 59 cells reexpressing cHSF1 (D2). (C) The cells shown in panel B were incubated at 43.5°C for 24 h, and representative cell cycle distributions are shown. (D) Wild-type (wt) and HSF1-null 59 (HSF1^−/−/−) cells were incubated for 24 h at the indicated temperatures. Proportions of sub-G₁ fractions are shown. Means and standard deviations of three independent experiments are shown. (E) Cells were incubated at 43.5°C for the indicated periods, and proportions of sub-G₁ fractions are shown as in panel D.