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 (PubMed:21262215, PubMed:1617729, PubMed:8674407, PubMed:10673509). Binds directly the 5'-GTGRGAR-3' DNA consensus sequence, which is present in the regulatory region of several genes (PubMed:10673509). Acts as a transcriptional repressor when it is not associated with Notch proteins (PubMed:10673509). When associated with some Notch protein, it acts as a transcriptional activator that activates transcription of Notch target genes (PubMed:10673509). Required for transcription of Sim (PubMed:10673509). Specifically binds to the immunoglobulin kappa-type J segment recombination signal sequence (PubMed:1744127, PubMed:1617730, PubMed:1617729). Required for neurogenesis in imaginal disks (PubMed:1617730, PubMed:7813798). In the larval brain, might play a role as a transducer of Notch signaling during type II neuroblast development (PubMed:21262215). Also functions independently of the Notch pathway, in the development of the bristle sensory organ precursor cell (PubMed:12642500). Interacts with activated cleaved Notch. Interacts with Hairless, this interaction preventing its DNA-binding activity. Interacts with insv (via BEN domain). In imaginal disk, at the onset of differentiation of socket cell, it is also present in the cytoplasm. Expressed in early syncytial embryo (PubMed:1617730, PubMed:1617729). During cellularization, transient accumulation in a striped pattern (PubMed:1617730, PubMed:1617729). From late stage 11 onward, expressed gradually in a small number of segmentally reiterated cells of the peripheral nervous system (PNS) (PubMed:1617730, PubMed:1617729). This expression is specific to the external sensory organs (PubMed:1617730). In the thoracic and abdominal segments, expressed in the trichogen and tormogen cells, two outer accessory cells present in all larval external sensory organs (PubMed:1617730). During the late third larval instar, expressed in many larval and imaginal tissues (PubMed:1617730). Broadly distributed in the disks, but most abundant in the posterior region of the wing pouch (PubMed:1617730). In the leg disk, predominant in a zone largely overlapping the posterior region (PubMed:1617730). In the eye-antenna disk, low level in both the retinal field posterior to the morphogenetic furrow and the central antenna region, while higher levels appears on the margins of the disk and in the vicinity of the morphogenetic furrow (PubMed:1617730). In pupae, expressed in many tissues at this stage, including developing muscle and epidermis (PubMed:1617730). In both microchaetes and macrochaetes of 24 hr pupae, expressed on the notum and the head (PubMed:1617730). Expressed in the tormogen cell and in specific bristle cells (PubMed:1617730). Lethal during the first day of pupal development (PubMed:1617730). At the larval stage, results in a 'neurogenic' phenotype in imaginal disks, in which too many cells adopt the sensory organ precursor cell fate (PubMed:1617730). RNAi-mediated knockdown in type II neuroblasts, results in smaller cells (PubMed:1617730). Belongs to the Su(H) family. Despite some similarity with the 'phage' integrase family, PubMed:7958912 showed that it has no recombinase activity. Truncated N-terminus.