Regulation of transcriptional activation by protein disorder PIs: Daughdrill/Chen Abstract The p53 tumor suppressor is a sequence-specific DNA binding protein that activates gene transcription to regulate cell survival and proliferation. It is mutated in at least 50% of solid tumors and some of these mutants are oncogenic and activate the transcription of genes that promote cell survival and metastasis. Despite decades of research on p53, there are currently no FDA approved drugs in the clinic that directly target wt or mutant p53. This is, in part, because 50% of p53 is disordered and we have an incomplete understanding of what these regions look like and how they function. We have recently shown that the disordered N-terminal acidic transactivation domain of p53 (NT) dynamically interacts with the DNA binding domain (DBD) with residues that contact DNA. This interaction inhibits DNA binding but increases binding specificity using a combination of nucleic acid mimicry and electrostatic shielding that enhances recognition of promoter binding sites in vivo. We propose to: (1) Determine the specific effects of nucleic acid mimicry and electrostatic shielding on DNA binding specificity, and how tethering controls the intramolecular interaction between NT and DBD. (2) Investigate how p53 NT phosphorylation regulates DNA binding affinity and specificity to create adaptable switching of transcriptional activation. (3) Determine how MdmX interferes with p53 DNA binding when it forms a heterodimer with p53. Successful completion of these experiments will lead to a better understanding of how p53 governs cell fate after DNA damage by regulating the binding specificity to pro-survival versus pro-apoptotic target genes. A deeper understanding of the structural and functional properties of the weak dynamic interactions within p53 and between p53 and MdmX is necessary for the successful development of small molecules to target these interactions for cancer therapy.