A SNARE-like protein required for traffic through the Golgi complex

The secretory pathway of eukaryotic cells comprises several distinct membrane-bound compartments which are interconnected by transport vesicles that pinch off from one membrane and fuse with the next. Targeting of these vesicles is mediated in part by interactions between integral membrane proteins on the vesicles and target organelles (soluble NSF attachment protein receptors (SNAREs)), termed v-SNAREs and t-SNAREs, respectively. SNAREs required for endoplasmic reticulum (ER)-Golgi transport and for fusion of vesicles with the plasma membrane are already known. Here we identify two yeast membrane proteins that show genetic interactions with Sed5p, which is the t-SNARE for ER-Golgi traffic. One of these membrane proteins, Sft1p, is structurally similar to the known v-SNAREs and is required for transport from an early to a later Golgi compartment. Our results indicate that a single t-SNARE can control more than one transport step, and provide the first candidate for a SNARE involved in intra-Golgi traffic.