title: Intracellular trafficking and ubiquitination of the Schizosaccharomyces pombe amino acid permease Aat1p.
abstract: In Schizosaccharomyces pombe, neither intracellular sorting nor ubiquitination of amino acid permeases is well understood. In the present study, we show that intracellular sorting of the amino acid permease Aat1p in S. pombe depends on the presence of a nitrogen source in the growth medium. Under nitrogen-sufficient conditions, Aat1p appeared to be stably localized at the Golgi apparatus. In contrast, under nitrogen-insufficient conditions, Aat1p was sorted to the plasma membrane. Over time, plasma membrane-localized Aat1p was internalized and sorted to the lumen of the vacuole, where it was degraded. Sorting of Aat1p to the vacuolar lumen was dependent on the ESCRT (endosomal sorting complex required for transport) complex, which is required for formation of the multivesicular body. S. pombe has three genes (pub1(+), pub2(+) and pub3(+)) that are homologous to the ubiquitin ligase RSP5. Under nitrogen-sufficient conditions, Aat1-GFP was missorted to the plasma membrane in pub1Δ cells and ubiquitinated Aat1p was not detected. These results suggest that Pub1p-mediated ubiquitination is required for retention of Aat1 at the Golgi under nitrogen-sufficient conditions. The Aat1p lysine mutant Aat1(K18, 26, 27) was completely missorted to the plasma membrane under nitrogen-rich conditions. Furthermore, Aat1(K4, 18R), Aat1(K4, 26, 27R) and Aat1(K18, 26, 27K) mutants were severely blocked in endocytosis. These results indicate that ubiquitination is an important determinant for localization and regulation of the Aat1p permease in S. pombe.
authors.affiliation: Department of Bioscience and Biotechnology, Faculty of Agriculture, Kyushu University, Hakozaki 6-10-1, Fukuoka 812-8581, Japan.
authors.forename: Mai
authors.initials: M
authors.lastname: Nakase
authors.affiliation: Department of Biostudies, Kyoto University, Kyoto 6060-8501, Japan.
authors.forename: Yukiko
authors.initials: Y
authors.lastname: Nakase
authors.affiliation: Department of Applied Bioresource Science, Faculty of Agriculture, Ehime University, Ehime 790-8566, Japan.
authors.forename: Soracom
authors.initials: S
authors.lastname: Chardwiriyapreecha
authors.affiliation: Department of Applied Bioresource Science, Faculty of Agriculture, Ehime University, Ehime 790-8566, Japan.
authors.forename: Yoshimi
authors.initials: Y
authors.lastname: Kakinuma
authors.affiliation: Department of Biostudies, Kyoto University, Kyoto 6060-8501, Japan.
authors.forename: Tomohiro
authors.initials: T
authors.lastname: Matsumoto
authors.affiliation: Department of Bioscience and Biotechnology, Faculty of Agriculture, Kyushu University, Hakozaki 6-10-1, Fukuoka 812-8581, Japan.
authors.forename: Kaoru
authors.initials: K
authors.lastname: Takegawa
mesh_terms: D026905:Amino Acid Transport Systems / Q000378:metabolism*; D002462:Cell Membrane / Q000737:chemistry; D003470:Culture Media / Q000737:chemistry; D006056:Golgi Apparatus / Q000737:chemistry; D009584:Nitrogen / Q000378:metabolism; D021381:Protein Transport; D012568:Schizosaccharomyces / Q000737:chemistry / Q000201:enzymology* / Q000378:metabolism*; D054875:Ubiquitination; D014617:Vacuoles / Q000737:chemistry
chemical_list: D026905:Amino Acid Transport Systems; D003470:Culture Media; D009584:Nitrogen