Different
packaging chaperones are required for ER exit of various hexose transporters in
Saccharomyces cerevisiae.
Tanja Hamacher,
Andreas Hippe, Eckhard Boles
Institut fuer Mikrobiologie, J.W.Goethe-Universitaet, Marie-Curie-Str. 9,
Frankfurt am Main, D-60439, Germany (Hamacher@em.uni-frankfurt.de)
In eukaryotic cells, membrane proteins are synthesized at and embedded into the membrane of the endoplasmatic reticulum (ER) before transported to their final destination membrane. They are transported from the ER to the Golgi-apparatus via ER-derived vesicles. A number of accessory proteins that are specifically required for the export of subsets of transporter proteins have been identified recently, and have been called packaging chaperones. One of these proteins is Gsf2 that functions in the ER to promote the secretion of certain hexose transporters to the yeast cell surface. In yeast cells the uptake of hexoses is mediated by a large family of 20 related transport proteins (Hxt-family). We investigated the role of Gsf2 on ER exit of all major Hxt proteins. Deletion of GSF2 resulted in the accumulation of some of the hexose transporters (e.g. Hxt1) in the ER whereas others (e.g. Hxt7) were normally delivered to the plasma membrane. Using the Split-Ubiquitin-System we could show that Gsf2 directly interacts with Hxt1. Chimeric constructs between Hxt1 and Hxt7 were used to determine those parts of the Hxt1 protein which are recognized by Gsf2. Moreover, we have developed a genetic screen to identify hep (Hxt ER packaging) mutant strains unable to deliver Hxt7 to the plasma membrane but retaining the transporter in the ER. We will report on the further characterization of these hep mutant strains and the Gsf2 protein.