title: The a-factor transporter (STE6 gene product) and cell polarity in the yeast Saccharomyces cerevisiae.
abstract: STE6 gene product is required for secretion of the lipopeptide mating pheromone a-factor by Saccharomyces cerevisiae MATa cells. Radiolabeling and immunoprecipitation, either with specific polyclonal antibodies raised against a TrpE-Ste6 fusion protein or with mAbs that recognize c-myc epitopes in fully functional epitope-tagged Ste6 derivatives, demonstrated that Ste6 is a 145-kD phosphoprotein. Subcellular fractionation, various extraction procedures, and immunoblotting showed that Ste6 is an intrinsic plasma membrane-associated protein. The apparent molecular weight of Ste6 was unaffected by tunicamycin treatment, and the radiolabeled protein did not bind to concanavalin A, indicating that Ste6 is not glycosylated and that glycosylation is not required either for its membrane delivery or its function. The amino acid sequence of Ste6 predicts two ATP-binding folds; correspondingly, Ste6 was photoaffinity-labeled specifically with 8-azido-[alpha-32P]ATP. Indirect immunofluorescence revealed that in exponentially growing MATa cells, the majority of Ste6 showed a patchy distribution within the plasma membrane, but a significant fraction was found concentrated in a number of vesicle-like bodies subtending the plasma membrane. In contrast, in MATa cells exposed to the mating pheromone alpha-factor, which markedly induced Ste6 production, the majority of Ste6 was incorporated into the plasma membrane within the growing tip of the elongating cells. The highly localized insertion of this transporter may establish pronounced anisotropy in a-factor secretion from the MATa cell, and thereby may contribute to the establishment of the cell polarity which restricts partner selection and cell fusion during mating to one MAT alpha cell.
authors.affiliation: Department of Molecular and Cell Biology, University of California, Berkeley 94720.
authors.forename: K
authors.initials: K
authors.lastname: Kuchler
authors.forename: H G
authors.initials: HG
authors.lastname: Dohlman
authors.forename: J
authors.initials: J
authors.lastname: Thorner
mesh_terms: D018528:ATP-Binding Cassette Transporters; D000255:Adenosine Triphosphate / Q000378:metabolism; D000595:Amino Acid Sequence; D001692:Biological Transport; D002462:Cell Membrane / Q000378:metabolism / Q000502:physiology* / Q000648:ultrastructure; D016764:Cell Polarity; D000939:Epitopes; D005656:Fungal Proteins / Q000276:immunology / Q000378:metabolism*; D015966:Gene Expression Regulation, Fungal; D006023:Glycoproteins; D000072235:Mating Factor; D008565:Membrane Proteins / Q000276:immunology / Q000502:physiology; D008969:Molecular Sequence Data; D010455:Peptides / Q000378:metabolism*; D010750:Phosphoproteins / Q000502:physiology; D012441:Saccharomyces cerevisiae / Q000502:physiology* / Q000648:ultrastructure; D029701:Saccharomyces cerevisiae Proteins
chemical_list: D018528:ATP-Binding Cassette Transporters; D000939:Epitopes; D005656:Fungal Proteins; D006023:Glycoproteins; D008565:Membrane Proteins; D010455:Peptides; D010750:Phosphoproteins; C489277:STE6 protein, S cerevisiae; D029701:Saccharomyces cerevisiae Proteins; D000072235:Mating Factor; D000255:Adenosine Triphosphate