p53 Response to Senescence Figure 2. Analysis of the p53-dependent transcriptional signature. A) Comparison of the levels of 122 transcriptional targets of p53 at different conditions of p53 activity. See text. Data normalized against b-actin were compared to the proliferative condition P3 to evaluate its statistical significance. Statistical analysis was performed by paired t-test. (*) = p,0.05; (**) = p,0.005; (***) = p,0.001. B) and C) Analysis of the expression values of 122 transcriptional targets of p53 under different cellular conditions, which led either to proliferation or to growth arrest. Clustering analysis. Hierarchical clustering was performed using the function hcluster (package amap) of the free statistical software R. See M & M. The expression level of each gene, relative to its median expression level across all conditions, was represented by a color, with red representing expression greater than the median, green representing expression less than the median, and the color intensity representing the magnitude of the deviation from the median. PLoS ONE | www.plosone.org 5 September 2008 | Volume 3 | Issue 9 | e3230