Ligands, structure and processing of Notch1 receptor. Left: the Delta-like ligand (Dll) and Serrate-Jagged ligand (Jag) structural subsets of Notch ligands. Right: structure of Notch1 receptor resulting from post-translational cleavage at site S1 and heterodimerization of the cleaved parts. Ligand-dependent cleavages at sites S2 and S3 generate soluble Notch extracellular truncation (NEXT) and cytosolic Notch intracellular domain (N-IC) forms, respectively. Notch1 and Notch2 are highly similar. Notch3 and Notch4 contain 34 and 29 epidermal growth factor (EGF)-like repeats, and are devoid of trans-activation domain (TAD) domains.