The α -Helical FXXΦ Φ Motif in p53: TAF Interaction and Discrimination by MDM2

Transcriptional activation domains share little sequence homology and generally lack folded structures in the absence of their targets, aspects that have rendered activation domains difficult to characterize. Here, a combination of biochemical and nuclear magnetic resonance experiments demonstrates that the activation domain of the tumor suppressor p53 has an FXXΦΦ motif (F, Phe; X, any amino acids; Φ, hydrophobic residues) that folds into an α-helix upon binding to one of its targets, hTAF_II31 (a human TFIID TATA box-binding protein-associated factor). MDM2, the cellular attenuator of p53, discriminates the FXXΦΦ motif of p53 from those of NF-κB p65 and VP16 and specifically inhibits p53 activity. Our studies support the notion that the FXXΦΦ sequence is a general α-helical recognition motif for hTAF_II31 and provide insights into the mechanistic basis for regulation of p53 function.