Organelle Membrane Fusion: A Novel Function for the Syntaxin Homolog Ufe1p in ER Membrane Fusion

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The fusion of endoplasmic reticulum (ER) membranes in yeast does not require Sec18p/NSF and Sec17p, two proteins needed for docking of vesicles with their target membrane. Instead, ER membranes require a NSF-related ATPase, Cdc48p. Since both vesicular and organelle fusion events use related ATPases, we investigated whether both fusion events are also SNARE mediated. We present evidence that the fusion of ER membranes requires Ufe1p, a t-SNARE that localizes to the ER, but no known v-SNAREs. We propose that the Ufe1 protein acts in the dual capacity of an organelle membrane fusion–associated SNARE by undergoing direct t-t-SNARE and Cdc48p interactions during organelle membrane fusion as well as a t-SNARE for vesicular traffic.