Figure 5: Effect of nicotine-free tobacco extract (1mg/mL) on pATM Ser-1981 focus formation in the nucleus. At the indicated time points, cells were collected for immunofluorescence analyses of pATM Ser-1981. A nucleus containing more than five foci is defined as a focus-positive cell. Values are means ± SEM, n = 3. *, p < 0.05; **, p < 0.01, compared to 0 h.