title: Ssh4, Rcr2 and Rcr1 affect plasma membrane transporter activity in Saccharomyces cerevisiae.
abstract: Nutrient uptake in the yeast Saccharomyces cerevisiae is a highly regulated process. Cells adjust levels of nutrient transporters within the plasma membrane at multiple stages of the secretory and endosomal pathways. In the absence of the ER-membrane-localized chaperone Shr3, amino acid permeases (AAP) inefficiently fold and are largely retained in the ER. Consequently, shr3 null mutants exhibit greatly reduced rates of amino acid uptake due to lower levels of AAPs in their plasma membranes. To further our understanding of mechanisms affecting AAP localization, we identified SSH4 and RCR2 as high-copy suppressors of shr3 null mutations. The overexpression of SSH4, RCR2, or the RCR2 homolog RCR1 increases steady-state AAP levels, whereas the genetic inactivation of these genes reduces steady-state AAP levels. Additionally, the overexpression of any of these suppressor genes exerts a positive effect on phosphate and uracil uptake systems. Ssh4 and Rcr2 primarily localize to structures associated with the vacuole; however, Rcr2 also localizes to endosome-like vesicles. Our findings are consistent with a model in which Ssh4, Rcr2, and presumably Rcr1, function within the endosome-vacuole trafficking pathway, where they affect events that determine whether plasma membrane proteins are degraded or routed to the plasma membrane.
authors.affiliation: Ludwig Institute for Cancer Research, S-171 77 Stockholm, Sweden.
authors.forename: Jhansi
authors.initials: J
authors.lastname: Kota
authors.forename: Monika
authors.initials: M
authors.lastname: Melin-Larsson
authors.forename: Per O
authors.initials: PO
authors.lastname: Ljungdahl
authors.forename: Hanna
authors.initials: H
authors.lastname: Forsberg
mesh_terms: D000595:Amino Acid Sequence; D026905:Amino Acid Transport Systems / Q000235:genetics / Q000378:metabolism; D002462:Cell Membrane / Q000378:metabolism; D011992:Endosomes / Q000378:metabolism; D005800:Genes, Fungal; D016153:Genes, Suppressor; D008565:Membrane Proteins / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism*; D026901:Membrane Transport Proteins / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism*; D008954:Models, Biological; D008969:Molecular Sequence Data; D009154:Mutation; D010957:Plasmids / Q000235:genetics; D011499:Protein Processing, Post-Translational / Q000187:drug effects; D012441:Saccharomyces cerevisiae / Q000187:drug effects / Q000235:genetics* / Q000378:metabolism*; D029701:Saccharomyces cerevisiae Proteins / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism*; D017386:Sequence Homology, Amino Acid; D020123:Sirolimus / Q000494:pharmacology; D014617:Vacuoles / Q000378:metabolism; D033921:Vesicular Transport Proteins
chemical_list: D026905:Amino Acid Transport Systems; C491145:GAP1 protein, S cerevisiae; D008565:Membrane Proteins; D026901:Membrane Transport Proteins; C498876:Rcr1 protein, S cerevisiae; C077883:SHR3 protein, S cerevisiae; D029701:Saccharomyces cerevisiae Proteins; C429825:TAT2 protein, S cerevisiae; D033921:Vesicular Transport Proteins; D020123:Sirolimus