MODIFICATION OF 2 DISTINCT COOH-TERMINAL DOMAINS IS REQUIRED FOR MURINE P53 ACTIVATION BY BACTERIAL HSP70

Activation of the latent DNA binding function of human p53 protein by the bacterial Hsp70, DnaK, represents a unique reaction in which a hea t shock protein can interact with a native protein to affect its funct ion, We have localized a likely DnaK interaction site on native human p53 tetramers to a motif flanking the COOH-terminal casein kinase II a nd protein kinase C phosphorylation sites, Murine p53 is less efficien tly activated by DnaK, which has permitted a search for factors that m ight cooperate in p53 activation by DnaK. We show that optimal activat ion by DnaK may be dependent upon the phosphorylation state of murine p53, in particular, modification of p53 at the cdc2 phosphorylation si te by point mutation decreases the extent of activation by DnaK. Addit ionally, the monoclonal antibody PAb241, binding in the vicinity of th e cdc2 phosphorylation site, is able to activate the specific DNA bind ing function of p53. This has led us to propose a second regulatory mo tif flanking the tetramerization domain of p53 that cooperates with fa ctors binding at the negative regulatory domain in the extreme COOH te rminus.