Genes that are induced in CLL cells after fludarabine treatment or irradiation are dependent on p53. Two isogenic cell lines that differ in their p53 loci only (TK6 with p53 wild-type alleles and NH32 with 2 null p53 alleles) were irradiated, and gene expression changes for selected genes are depicted relative to their pretreatment levels (black squares) according to the color scheme shown in Figure 4.