**Figure 4.** **DSB-related DDR.** **(A**) H2AX phosphorylation was determined in dermal fibroblasts by immune blotting [**B**) Cross-comparison of base line H2AX phosphorylation (in the absence of VP16, same data as represented by open symbols in section A of this figure) and frequency of structural chromosome aberrations (same data as shown in Fig. **A, B**) Results of linear regression are stated as R^{2}: Pearson's coefficient for goodness of fit, p: probability for slope = 0, dotted lines: 95% confidence limits of linear regression, and *N.S*.: linear regression of the data revealed no significant age-related change in the parameters.