ACTIVATION OF P53 DNA-BINDING ACTIVITY BY POINT MUTATION

The p53 tumor suppressor protein can adopt both latent, non-DNA bindin g and active, DNA binding forms, and p53 activity is thought to be reg ulated in cells, at least in part, through a conformational shift whic h leads to sequence specific DNA binding. In vitro, this allosteric re gulation of DNA binding by p53 has been shown to be mediated through t he C-terminus of the protein. We show here that although deletion of t he C-terminal 16 amino acids of p53 did not activate DNA binding, dele tion of a further eight amino acids resulted in constitutive activatio n of DNA binding activity. Simultaneous mutation of the three lysine r esidues within these eight amino acids also resulted in constitutive D NA binding activity, although this was reduced when only two of these lysines were altered, The deletion or point mutants of p53 showing con stitutive DNA binding activity did not display clear evidence of DNA b inding site specificity, although some binding site preference was see n with the point mutants. Each of the constitutively active p53 mutant s retained transcriptional activity and induced both cell cycle arrest and apoptosis in transiently transfected cells at rates comparable wi th the wild type protein.