Ligand activation of Notch leads to the release of Notch IC (the intracellular receptor domain), which translocates to the nucleus and interacts with the DNA-binding protein CSL to control expression of specific target genes. In addition to ligand-mediated activation, Notch signalling can be further modulated by interactions of Notch IC with a number of other proteins. MAML1 has previously been shown to act co-operatively with the histone acetyltransferase p300 in Notch IC-mediated transcription. In the present study we show that the N-terminal domain of MAML1 directly interacts with both p300 and histones, and the p300-MAML1 complex specifically acetylates histone H3 and H4 tails in chromatin. Furthermore, p300 acetylates MAML1 and evolutionarily conserved lysine residues in the MAML1 N-terminus are direct substrates for p300-mediated acetylation. The N-terminal domain of MAML1 contains a proline repeat motif (PXPAAPAP) that was previously shown to be present in p53 and important for the p300-p53 interaction. We show that the MAML1 proline repeat motif interacts with p300 and enhances the activity of the MAML1 N-terminus in vivo. These findings suggest that the N-terminal domain of MAML1 plays an important role in Notch-regulated transcription, by direct interactions with Notch, p300 and histones.