Notch receptors transduce essential developmental signals between neighboring 
cells by forming a complex that leads to transcription of target genes upon 
activation. We report here the crystal structure of a Notch transcriptional 
activation complex containing the ankyrin domain of human Notch1 (ANK), the 
transcription factor CSL on cognate DNA, and a polypeptide from the coactivator 
Mastermind-like-1 (MAML-1). Together, CSL and ANK create a groove to bind the 
MAML-1 polypeptide as a kinked, 70 A helix. The composite binding surface likely 
restricts the recruitment of MAML proteins to promoters on which Notch:CSL 
complexes have been preassembled, ensuring tight transcriptional control of 
Notch target genes.