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The p53 tumor suppressor protein can adopt both latent, non-DNA binding and active, DNA binding forms, and p53 activity is thought to be regulated in cells, at least in part, through a conformational shift which leads to sequence specific DNA binding. In vitro, this allosteric regulation of DNA binding by p53 has been shown to be mediated through the C-terminus of the protein. We show here that although deletion of the C-terminal 16 amino acids of p53 did not activate DNA binding, deletion of a further eight amino acids resulted in constitutive activation of DNA binding activity. Simultaneous mutation of the three lysine residues within these eight amino acids also resulted in constitutive DNA binding activity, although this was reduced when only two of these lysines were altered. The deletion or point mutants of p53 showing constitutive DNA binding activity did not display clear evidence of DNA binding site specificity, although some binding site preference was seen with the point mutants. Each of the constitutively active p53 mutants retained transcriptional activity and induced both cell cycle arrest and apoptosis in transiently transfected cells at rates comparable with the wild type protein. [ABSTRACT FROM AUTHOR]