title: The vacuolar kinase Yck3 maintains organelle fragmentation by regulating the HOPS tethering complex.
abstract: The regulation of cellular membrane flux is poorly understood. Yeast respond to hypertonic stress by fragmentation of the normally large, low copy vacuole. We used this phenomenon as the basis for an in vivo screen to identify regulators of vacuole membrane dynamics. We report here that maintenance of the fragmented phenotype requires the vacuolar casein kinase I Yck3: when Yck3 is absent, salt-stressed vacuoles undergo fission, but reassemble in a SNARE-dependent manner, suggesting that vacuole fusion is disregulated. Accordingly, when Yck3 is deleted, in vitro vacuole fusion is increased, and Yck3 overexpression blocks fusion. Morphological and functional studies show that Yck3 modulates the Rab/homotypic fusion and vacuole protein sorting complex (HOPS)-dependent tethering stage of vacuole fusion. Intriguingly, Yck3 mediates phosphorylation of the HOPS subunit Vps41, a bi-functional protein involved in both budding and fusion during vacuole biogenesis. Because Yck3 also promotes efficient vacuole inheritance, we propose that tethering complex phosphorylation is a part of a general, switch-like mechanism for driving changes in organelle architecture.
authors.affiliation: Biochemie-Zentrum der Universität Heidelberg, 69120 Heidelberg, Germany.
authors.forename: Tracy J
authors.initials: TJ
authors.lastname: LaGrassa
authors.forename: Christian
authors.initials: C
authors.lastname: Ungermann
mesh_terms: D033942:Adaptor Proteins, Vesicular Transport; D000906:Antibodies / Q000494:pharmacology; D047389:Casein Kinase I / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005838:Genotype; D020730:Guanine Nucleotide Dissociation Inhibitors / Q000494:pharmacology; D008387:Marine Toxins; D008561:Membrane Fusion / Q000187:drug effects / Q000502:physiology; D008565:Membrane Proteins / Q000276:immunology / Q000378:metabolism; D052998:Microcystins; D008856:Microscopy, Fluorescence; D008954:Models, Biological; D009154:Mutation; D009419:Nerve Tissue Proteins / Q000276:immunology; D015388:Organelles / Q000378:metabolism / Q000502:physiology; D010456:Peptides, Cyclic / Q000494:pharmacology; D010766:Phosphorylation; D017853:Phosphotransferases (Alcohol Group Acceptor) / Q000235:genetics; D050600:SNARE Proteins; D012441:Saccharomyces cerevisiae / Q000187:drug effects / Q000235:genetics / Q000502:physiology*; D029701:Saccharomyces cerevisiae Proteins / Q000819:agonists / Q000037:antagonists & inhibitors / Q000235:genetics / Q000276:immunology / Q000378:metabolism / Q000502:physiology*; D012462:Saline Solution, Hypertonic / Q000494:pharmacology; D050825:Synaptosomal-Associated Protein 25; D014617:Vacuoles / Q000378:metabolism / Q000502:physiology*; D033921:Vesicular Transport Proteins / Q000235:genetics / Q000276:immunology / Q000378:metabolism / Q000502:physiology*; D020691:rab GTP-Binding Proteins / Q000037:antagonists & inhibitors / Q000276:immunology; D020703:ras GTPase-Activating Proteins / Q000819:agonists
chemical_list: D033942:Adaptor Proteins, Vesicular Transport; D000906:Antibodies; D004791:Enzyme Inhibitors; C086796:GDP dissociation inhibitor 1; D020730:Guanine Nucleotide Dissociation Inhibitors; C439608:Gyp7 protein, S cerevisiae; D008387:Marine Toxins; D008565:Membrane Proteins; D052998:Microcystins; D009419:Nerve Tissue Proteins; D010456:Peptides, Cyclic; D050600:SNARE Proteins; D029701:Saccharomyces cerevisiae Proteins; D012462:Saline Solution, Hypertonic; D050825:Synaptosomal-Associated Protein 25; C406817:VAM6 protein, S cerevisiae; C065531:VPS3 protein, S cerevisiae; C083878:VPS41 protein, S cerevisiae; D033921:Vesicular Transport Proteins; D020703:ras GTPase-Activating Proteins; C095504:FAB1 protein, S cerevisiae; D017853:Phosphotransferases (Alcohol Group Acceptor); D047389:Casein Kinase I; C479667:YCK3 protein, S cerevisiae; C079005:YPT7 protein, S cerevisiae; D020691:rab GTP-Binding Proteins; C057862:cyanoginosin LR