Transcriptional regulator that plays a central role in Notch signaling, a signaling pathway involved in cell-cell communication that regulates a broad spectrum of cell-fate determinations. Acts as a transcriptional repressor when it is not associated with Notch proteins. When associated with some Notch protein, it acts as a transcriptional activator that activates transcription of Notch target genes (By similarity). Required for the transcriptional expression of Brachyury, suggesting that it participates in notochord differentiation. Interacts with activated Notch proteins. Belongs to the Su(H) family.