p53 latency - C-terminal domain prevents binding of p53 core to target butnot to nonspecific DNA sequences

The p53 transcription factor is either latent or activated through multi-si te phosphorylation and acetylation of the negative regulatory region in its C-terminal domain (CTD). How CTD modifications activate p53 binding to tar get DNA sequences via its core domain is still unknown. It has been propose d that nonmodified CTD interacts either with the core domain or with DNA pr eventing binding of the core domain to DNA and that the fragments of the CT D regulatory region activate p53 by interfering with these interactions. We here characterized the sequence and target specificity of p53 activation b y CTD fragments, interaction of activating peptides with p53 and target DNA , and interactions of "latent" p53 with. DNA by a band shift assay and by f luorescence correlation spectroscopy. In addition to CTD fragments, several long basic peptides activated p53 and also transcription factor YY1. These peptides and CTD aggregated target DNA but apparently did not interact wit h p53. The potency to aggregate DNA correlated with the ability to activate p53, suggesting that p53 binds to target sequences upon interactions with tightly packed DNA in aggregates. Latent full-length p53 dissociated DNA ag gregates via its core and CTD, and this effect was potentiated by GTP. Late nt p53 also formed complexes via both its core and CTD with long nontarget DNA molecules. Such p53-DNA interactions may occur if latent p53 binding to DNA via CTD prevents the interaction of the core domain with target DNA si tes but not with nonspecific DNA sequences.