SNARE-mediated retrograde traffic from the Golgi complex to the endoplasmic reticulum

Operation of the secretory pathway in eukaryotic cells requires the selective docking and fusion of transport vesicles with the appropriate target organelle. This is mediated in part by integral membrane proteins termed v-SNAREs (on vesicles) and t-SNAREs (on the target membranes). We describe a novel yeast t-SNARE that resides on the endoplasmic reticulum and mediates retrograde traffic from the Golgi complex. Mutation of this protein prevents both the HDEL receptor and a membrane protein bearing a dibasic retrieval signal from recycling to the endoplasmic reticulum. Forward traffic is also blocked, but only indirectly. Comparison with other yeast mutants indicates that Sec21p (gamma-COP) and Sec20p (an endoplasmic reticulum membrane protein) are also involved primarily, if not exclusively, in retrograde transport.