Regulation of the cryptic sequence-specific DNA-binding function of p53 by protein kinases

p53 is an allosterically regulated protein with a latent DNA-binding activity. Posttranslational modification of a carboxy-terminal regulatory site in vitro, by casein kinase II and protein kinase C, can activate the sequence-specific DNA-binding function of the wild-type protein. The latent form of p53 is produced in a variety of eukaryotic and prokaryotic cell lines, including E. coli, Sf9 insect cells, and C6 cells, indicating that the activation of p53 in vivo is rate-limiting. In addition, phosphorylation of p53 at the protein kinase C site and activation in vivo correlate with the loss of reactivity of active p53 protein to the carboxy-terminal antibody, PAb421. These results suggest that two highly conserved protein kinases modify polypeptide structure through a common biochemical mechanism and that different enzymatic pathways may channel information into the carboxy-terminal regulatory site of p53, allosterically activating its function as a tumor suppressor.