title: Connection between the Rag4 glucose sensor and the KlRgt1 repressor in Kluyveromyces lactis.
abstract: The RAG4 gene encodes for the sole transmembrane glucose sensor of Kluyveromyces lactis. A rag4 mutation leads to a fermentation-deficient phenotype (Rag- phenotype) and to a severe defect in the expression of the major glucose transporter gene RAG1. A recessive extragenic suppressor of the rag4 mutation has been identified. It encodes a protein (KlRgt1) 31% identical to the Saccharomyces cerevisiae Rgt1 regulator of the HXT genes (ScRgt1). The Klrgt1 null mutant displays abnormally high levels of RAG1 expression in the absence of glucose but still presents an induction of RAG1 expression in the presence of glucose. KlRgt1 is therefore only a repressor of RAG1. As described for ScRgt1, the KlRgt1 repressor function is controlled by phosphorylation in response to high glucose concentration and this phosphorylation is dependent on the sensor Rag4 and the casein kinase Rag8. However, contrary to that observed with ScRgt1, KlRgt1 is always bound to the RAG1 promoter. This article reveals that the key components of the glucose-signaling pathway are conserved between S. cerevisiae and K. lactis, but points out major differences in Rgt1 regulation and function that might reflect different carbon metabolism of these yeasts.
authors.affiliation: Génétique des Levures, UMR 5122 Microbiologie et Génétique, Université Claude Bernard Lyon 1, 69622 Villeurbanne, France.
authors.forename: Stéphane
authors.initials: S
authors.lastname: Rolland
authors.forename: Martina
authors.initials: M
authors.lastname: Hnatova
authors.forename: Marc
authors.initials: M
authors.lastname: Lemaire
authors.forename: Juana
authors.initials: J
authors.lastname: Leal-Sanchez
authors.forename: Micheline
authors.initials: M
authors.lastname: Wésolowski-Louvel
mesh_terms: D000595:Amino Acid Sequence; D005656:Fungal Proteins / Q000037:antagonists & inhibitors / Q000235:genetics / Q000502:physiology*; D005947:Glucose / Q000378:metabolism*; D018398:Homeodomain Proteins / Q000037:antagonists & inhibitors / Q000096:biosynthesis / Q000235:genetics; D007716:Kluyveromyces / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D008969:Molecular Sequence Data; D011401:Promoter Regions, Genetic; D011485:Protein Binding / Q000235:genetics; D012097:Repressor Proteins / Q000502:physiology*; D029701:Saccharomyces cerevisiae Proteins / Q000235:genetics / Q000502:physiology; D015534:Trans-Activators / Q000502:physiology
chemical_list: D005656:Fungal Proteins; D018398:Homeodomain Proteins; C435343:RAG4 protein, Kluyveromyces; D012097:Repressor Proteins; D029701:Saccharomyces cerevisiae Proteins; D015534:Trans-Activators; C064658:RAG-1 protein; D005947:Glucose