Sequence-specific DNA binding by p53: identification of target sites and lack of binding to p53 - MDM2 complexes.

An immune selection procedure was employed in order to isolate p53 binding sites from mouse genomic DNA. Two DNA clones capable of tight specific interaction with wild type p53 were subjected to further characterization. In both cases, the p53 binding regions displayed a high degree of sequence homology with the consensus binding site defined for human genomic DNA. One of the clones was found to be derived from the LTR of a retrovirus-like element (a member of the GLN family). The region encompassing the GLN LTR p53 binding site could confer p53 responsiveness upon a heterologous promoter. Furthermore, the expression of the endogenous, chromosomally integrated GLN elements was significantly induced upon activation of wild type p53 in cells harboring a temperature sensitive p53 mutant. Finally, it was demonstrated that p53 - MDM2 complexes fail to bind tightly to such a p53 binding site. This may contribute to the inhibition by MDM2 of p53-mediated transcriptional activation.