SED5 encodes a Qa SNARE required for ER-Golgi and intra-Golgi trafficking steps where it functions in vesicle fusion in yeast. Understanding the mechanism(s) by which Sed5p is localized to the Golgi will provide insight into the biogenesis and maintenance of this organelle. Like other members of the Syntaxin family, Sed5p is a type Il membrane protein comprised of a SNARE motif and a N-terminal regulatory motif termed Habc domain. The SNARE and Habc domain can associate with one another adopting a closed conformation. Here I provide evidence that a novel COPI interacting motif is present at the N-terminus of Sed5p. Furthermore, the association of the Habc domain and the SNARE motif is crucial for Sed5p's localization to the cis-Golgi. I propose that Sed5p's rapid recycling to the ER is...[ Read more ]

SED5 encodes a Qa SNARE required for ER-Golgi and intra-Golgi trafficking steps where it functions in vesicle fusion in yeast. Understanding the mechanism(s) by which Sed5p is localized to the Golgi will provide insight into the biogenesis and maintenance of this organelle. Like other members of the Syntaxin family, Sed5p is a type Il membrane protein comprised of a SNARE motif and a N-terminal regulatory motif termed Habc domain. The SNARE and Habc domain can associate with one another adopting a closed conformation. Here I provide evidence that a novel COPI interacting motif is present at the N-terminus of Sed5p. Furthermore, the association of the Habc domain and the SNARE motif is crucial for Sed5p's localization to the cis-Golgi. I propose that Sed5p's rapid recycling to the ER is mediated by the direct contacts between the ER and the Golgi. While the COPI interacting motif functions as a failsafe to capture the Sed5p that has leaked to distal compartments and return the protein to the cis-Golgi.