p53 binding ability of 29-bp sequence. (A) Ability of 29-bp sequence to compete p53 binding in extracts. Extracts of irradiated T10 cells are tested on gel-shift assay. The upstream p53 site in the p21 promoter (2.4) is targeted. The first two lanes demonstrate the appearance of the expected p53 gel-shift band in the presence of anti-p53 antibody pAb421. The p53 band is partially competed by 100-fold excess of 29-bp sequence but not mutated sequence (M4). (B) Lack of direct binding of p53 to the 29-bp sequence. A gel-shift assay is shown demonstrating binding of recombinant p53 core protein to the upstream p53 site (2.4) but not to the 29-bp sequence.