Function of the Drosophila TGF-alpha homolog Spitz is controlled by Star and interacts directly with Star

Drosophila Spitz is a homolog of transforming growth factor alpha (TGF-alph a) and is an activating ligand for the EGF receptor (Egfr). It has been sho wn that Star is required for Spitz activity. Here we show that Star is quan titatively limiting for Spitz production during eye development. We also sh ow that Star and Spitz proteins colocalize in Spitz sending cells and that this association is not coincident with the site of translation consistent with a function for Star in Spitz processing or transmission. Finally, we h ave defined minimal sequences within both Spitz and Star that mediate a dir ect interaction and show that this binding can occur in vivo. (C) 2001 Else vier Science Ireland Ltd. All rights reserved.