Distance constraints and stereospecific alignment requirements characteristic of p53 DNA-binding consensus sequence homologies.

We present evidence in favor of the position that some mutant p53 proteins retain the ability to trans-activate downstream genes through p53 DNA-binding consensus sequence (CS) homologies. We tested one cell line possessing high levels of mutant p53 and found that this mutant p53 is highly active in trans-activating one CS homology, moderately active in trans-activating a second sequence and inactive in modulating a third sequence. We tested a second cell line, also possessing high levels of mutant p53 and found the same pattern of activation. In addition we find that inter-motif distance [represented by N in RRRCWWGYYY(N)RRRCWWGYYY] is very important in determining the relative binding affinity of a given CS homology for wild-type or mutant p53. Our studies suggest that stereospecific alignment of the DNA-binding motifs within the CS may favor binding of wild-type p53 while misalignment may favor binding of mutant p53. Furthermore, we find that the maximum distances at which p53 DNA-binding CS homologies are functionally active vary for different sequences. Introduction of as few as 200 bp between one CS homology and the downstream TATA box can eliminate a 45-fold p53-mediated transactivation. We present evidence that the composition of the DNA which flanks a p53 DNA-binding consensus sequence may also modulate trans-activation.