A YEAST T-SNARE INVOLVED IN ENDOCYTOSIS

The ORF YOL018c (TLG2) of Saccharomyces cerevisiae encodes a protein t hat belongs to the syntaxin protein family. The proteins of this famil y, t-SNAREs, are present on target organelles and are thought to parti cipate in the specific interaction between vesicles and acceptor membr anes in intracellular membrane trafficking. TLG2 is not an essential g ene, and its deletion does not cause defects in the secretory pathway. However, its deletion in cells lacking the vacuolar ATPase subunit Vm a2p leads to loss of viability, suggesting that Tlg2p is involved in e ndocytosis. In tlg2 Delta cells, internalization was normal for two en docytic markers, the pheromone alpha-factor and the plasma membrane ur acil permease. In contrast, degradation of alpha-factor and uracil per mease was delayed in tlg2 Delta cells. Internalization of positively c harged Nanogold shows that the endocytic pathway is perturbed in the m utant, which accumulates Nanogold in primary endocytic vesicles and sh ows a greatly reduced complement of early endosomes. These results str ongly suggest that Tlg2p is a t-SNARE involved in early endosome bioge nesis.