THE lin-12 and glp-1 genes of Caenorhabditis elegans are members of the lin-12/Notch family of receptors for intercellular signals that specify cell fate(1,2). By screening for suppressors of a lin-12 gain-of-function mutation, we identified a new gene, sel-12, which appears to function in receiving cells to facilitate signalling mediated by lin-12 and glp-1. The sel-12 gene encodes a protein with multiple transmembrane domains, and is similar to S182, which has been implicated in early-onset familial Alzheimer’s disease(3). The high degree of sequence conservation suggests that the function of the SEL-12 and S182 proteins may also be conserved.