DNA binding activity of p53 protein in AML cell lines. Nuclear extracts prepared from untreated or γ-irradiated OCI/AML-5 (A) and OCI/AML-3 (B) cells were incubated with a³²P-labeled double-stranded oligonucleotide containing the p53 consensus sequence (p53CON) with (+) or without (−) the p53-specific monoclonal antibody PAb421 and analyzed by EMSA. Lan1 cells, which lack p53 protein, were used as a negative control. The OCI/AML-5 and Lan1 extracts were prepared 3 hours after γ-irradiation with a dose of 6 Gy. The OCI/AML-3 extracts were prepared at the times indicated after γ-irradiation with a dose of 2 Gy. The arrow labeled B points to the p53:DNA complex, and the arrow labeled A points to the supershifted antibody:p53:DNA complex.