Loss-of-function of the tumour suppressor gene lethal (2) giant discs (lgd) in Drosophila results in the ligand-independent activation of the Notch signalling pathway and the overproliferation of imaginal disc cells. The Lgd protein contains a C2 domain – which can mediate binding to phospholipids or phosphorylated proteins – as well as four tandem DM14 domains of unknown function, and is involved in constitutive trafficking and degradation of Notch through the endosomal system. But how does Lgd affect endosome trafficking? Thomas Klein and co-workers (p. 763) provide an answer by using genetic and biochemical approaches to further characterise the tumour suppressor and its binding partners. They report that the C2 domain is required for stabilising Lgd and targeting it to the cytosol. The DM14 domains are required to provide specific protein function by interacting with other proteins, and largely act in a redundant manner. Specifically, the authors identify the interaction of the Lgd DM14 domains with the ESCRT-III-complex component Shrub (the Drosophila homologue of Snf7/CHMP4/Vps32). This interaction – which takes place in the cytosol – is required for Shrub function and shows that Lgd has an essential role in the regulation of endosomal trafficking.