Protein p53 modulates transcription from a promoter containing its binding site in a concentration-dependent manner.

Tumor suppressor protein p53 binds to DNA in a sequence-specific manner and activates transcription from promoters near its binding site. It is also known to repress promoters lacking the p53-binding site. In this study, we demonstrate that p53 can act as a transcriptional activator or repressor in vivo using the same reporter with the DNA-binding site CON and these effects depend on the amount of p53 expressed. Both in Saos2 and Cos7 cells, lower concentrations of p53 lead to activation and higher concentrations lead to repression of the model promoter containing the consensus p53-binding site CON. The N-terminal part of p53 is necessary for the transcriptional activation. It is not needed, however, for the repression of the same promoter, indicating that different domains of p53 are involved in activation and repression.