p53 binds to the BCL6 p53RE in vitro and in vivo. (A) p53 in vitro binding to the BCL6 p53RE was assayed by EMSA. Wild-type (lanes 2-6, 8) and mutant (lane 7) p53 proteins were incubated with the specified oligos. Oligo A, wild-type BCL6 p53RE (lanes 1-3, 5-7); Oligo B, like oligo A without the extra guanosine in the middle of the first decamer of the BCL6 p53RE (lane 4); Oligo C, mutated BCL6 p53RE (lane 8); supershift with anti-p53 antibody (lane 3); competition with a 50-fold or 500-fold excess of unlabeled oligo A (lanes 5 and 6, respectively). Ab indicates antibody. ×'sA indicates an excess of unlabeled Oligo A. (B) p53 in vivo binding to the BCL6 p53RE was assayed by ChIP in lymphoblastoid B cells. Immunoprecipitation of p53 protein-DNA complexes was done with anti-p53 antibody. Negative controls were chromatin immunoprecipitated with an irrelevant antibody (anti-GFP) and normal mouse IgG, as well as samples to which no antibody was added (no Ab). Positive control was chromatin immunoprecipitated with anti-RNA polymerase II antibody. Primers specific for the CDKN1A promoter and GAPDH exon 4 served as positive and negative controls, respectively. Input indicates 0.1% of the sonicated chromatin before immunoprecipitation.