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. Binds directly the 5'-GTGRGAR-3' DNA consensus sequence, which is present in the regulatory region of several genes. Required for neurogenesis in imaginal disks. 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. Probably represses or activates transcription via the recruitment of chromatin remodeling complexes containing histone deacetylase or histone acetylase proteins, respectively. Specifically binds to the immunoglobulin kappa-type J segment recombination signal sequence. Required for transcription of Sim. Also functions independently of Notch pathway, in the development of the bristle sensory organ precursor cell (By similarity). Interacts with activated Notch. Interacts with Hairless, this interaction preventing its DNA-binding activity. Interacts with insv (via BEN domain) (By similarity). In imaginal disk, at the onset of differentiation of socket cell, it is also present in the cytoplasm. Belongs to the Su(H) family.