Signaling protein, which regulates, with both positive and negative signals, the differentiation of at least central and peripheral nervous system and eye, wing disk, oogenesis, segmental appendages such as antennae and legs, and muscles, through lateral inhibition or induction. Functions as a receptor for membrane-bound ligands Delta and Serrate to regulate cell-fate determination. Upon ligand activation, and releasing from the cell membrane, the Notch intracellular domain (NICD) forms a transcriptional activator complex with Su(H) (Suppressor of hairless) and activates genes of the E(spl) complex. Essential for proper differentiation of ectoderm. Fringe (fng) acts in the Golgi to determine the type of O-linked fucose on the EGF modules in N, altering the ability of N to bind with Delta (Dl). O-fut1 also has a role in modulating the interaction. Rumi acts in the endoplasmic reticulum to glucosylate the EGF modules in N, this is required for correct folding and cleavage of N.