SEQUENCE-SPECIFIC DNA-BINDING BY P53 - IDENTIFICATION OF TARGET SITESAND LACK OF BINDING TO P53MDM2 COMPLEXES

An immune selection procedure was employed in order to isolate p53 bin ding sites from mouse genomic DNA. Two DNA clones capable of tight spe cific interaction with wild type p53 were subjected to further charact erization. In both cases, the p53 binding regions displayed a high deg ree of sequence homology with the consensus binding site defined for h uman genomic DNA. One of the clones was found to be derived from the L TR of a retrovirus-like element (a member of the GLN family). The regi on encompassing the GLN LTR p53 binding site could confer p53 responsi veness upon a heterologous promoter. Furthermore, the expression of th e endogenous, chromosomally integrated GLN elements was significantly induced upon activation of wild type p53 in cells harboring a temperat ure sensitive p53 mutant. Finally, it was demonstrated that p53-MDM2 c omplexes fail to bind tightly to such a p53 binding site. This may con tribute to the inhibition by MDM2 of p53-mediated transcriptional acti vation.