p53 is a conformationally flexible sequence-specific DNA binding protein mutated in many human tumors. To understand why the mutant p53 proteins associated with human tumors fail to bind DNA, we mapped the DNA binding domain of wild-type p53 and examined its regulation by changes in the protein conformation. Using site-directed mutagenesis, residues 90-286 of mouse p53 were shown to form the sequence-specific DNA binding domain. Two highly conserved regions within this domain, regions IV and V, were implicated in contacting DNA. Wild-type p53 bound DNA as a tetramer, each subunit recognizing five nucleotides of the 20 nucleotide-long DNA site. Conformational shifts of the oligomerization domain propagated to the tetrameric DNA binding domain, regulating DNA binding activity, but did not affect the subunit stoichiometry of wild-type p53 oligomers. Interestingly, conformational shifts could also be propagated within certain p53 mutants, rescuing DNA binding. One of these mutants was the mouse equivalent of human histidine 273, which is frequently associated with human tumors.