Tlg2p, a Yeast Syntaxin Homolog That Resides on the Golgi and Endocytic Structures

Intracellular membrane fusion events in eukaryotic cells are thought to be mediated by protein-protein interactions between soluble N-ethylmaleimide-sensitive factor attachment protein receptor (SNARE) complex proteins. We have identified and analyzed a new yeast syntaxin homolog, Tlg2p. Tlg2p is unique among known syntaxin family proteins in possessing a sizeable hydrophilic domain of 63 amino acids that is C-terminal to the membrane spanning region and nonessential for Tlg2p function. Tlg2p resides on the endosome and late Golgi by co-localization with an endocytic intermediate and co-fractionation with markers for both endosomes and late Golgi. Cells depleted for Tlg2p missort a portion of carboxypeptidase Y and are defective in endocytosis. In addition, we report that Tlg2p forms a SEC18-dependent SNARE complex with Snc2p, a vesicle SNARE known to function in Golgi to plasma membrane trafficking. Based on these findings we propose that Tlg2p is a t-SNARE that functions in transport from the endosome to the late Golgi and on the endocytic pathway.