DNA-BINDING SPECIFICITY OF PROTEINS DERIVED FROM ALTERNATIVELY SPLICED MOUSE P53 MESSENGER-RNAS

The mouse p53 gene generates two alternative splice products encoding p53 protein and a naturally occurring protein (p53as) with changes at the C-terminus: In p53as the negative regulatory region for DNA bindin g and PAb421 antibody binding site are replaced, and p53as is constitu tively active for sequence-specific DNA binding. Using the technique o f randomized synthetic oligonucleotide in cyclic amplification and sel ection of targets, we have found that p53as and p53 proteins have the same DNA binding specificities but that these specificities frequently diverge from the consensus of two copies of PuPuPuCATGPyPyPy. The imp ortance of tetranucleotide CATG was confirmed but there was a less rig orous requirement for patterns of flanking or intervening sequences. I n particular, the three purines upstream and three pyrimidines downstr eam of CATG are not required for p53 or p53as binding, 29 or more inte rvening nucleotides are tolerated, and one CATG is sufficient where ad jacent nucleotides contain a region of homology with certain previousl y reported non-consensus p53 binding sequences. These results suggeste d further definition of the non-consensus motifs, and database searche s with these uncovered additional candidate genes for p53 protein bind ing. We conclude that p53as and perhaps other activated forms of p53 e xert their effects on the same genes and that differential activities of p53 protein forms are not due to inherently different sequence sele ctivities of DNA binding.