Sprouty, an intracellular inhibitor of Ras signaling.

Sprouty was identified in a genetic screen as an inhibitor of Drosophila EGF receptor signaling. The Egfr triggers cell recruitment in the eye, and sprouty- eyes have excess photoreceptors, cone cells, and pigment cells. Sprouty's function is, however, more widespread. We show that it also interacts genetically with the receptor tyrosine kinases Torso and Sevenless, and it was first discovered through its effect on FGF receptor signaling. In contrast to an earlier proposal that Sprouty is extracellular, we show by biochemical analysis that Sprouty is an intracellular protein, associated with the inner surface of the plasma membrane. Sprouty binds to two intracellular components of the Ras pathway, Drk and Gap1. Our results indicate that Sprouty is a widespread inhibitor of Ras pathway signal transduction.