Mechanisms of ligand-independent ICN1 production in T-ALLs bearing Notch1 deletions. (A-B) Structure and functional consequences of type 1 and type 2 Notch1 deletions. (C) Conservation of M1727 in vertebrate Notch1 receptors. *Identical residues. “:” indicates conserved residues. TM indicates transmembrane domain; S3, site of intramembranous γ-secretase cleavage; and ICN, intracellular Notch.