"All Good Things Must Come to an End"

Turning off signaling pathways can be just as important for proper biological regulation as turning them on. The Notch signaling pathway controls development of the nervous system in Drosophila. Proteolysis of Notch appears to initiate signaling, but further proteolysis may also terminate signals from this pathway. Kopan discusses mechanisms that limit signaling by Notch, including recent evidence that degradation of specifically targeted proteins by the proteasome is required.