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Full-Text Articles in Medical Biochemistry
Sec17 Can Trigger Fusion Of Trans-Snare Paired Membranes Without Sec18, Michael Zick, Amy Orr, Matthew L. Schwartz, Alexey J. Merz, William Wickner
Sec17 Can Trigger Fusion Of Trans-Snare Paired Membranes Without Sec18, Michael Zick, Amy Orr, Matthew L. Schwartz, Alexey J. Merz, William Wickner
Dartmouth Scholarship
Sec17 [soluble N-ethylmaleimide-sensitive factor (NSF) attachment protein; α-SNAP] and Sec18 (NSF) perform ATP-dependent disassembly of cis-SNARE complexes, liberating SNAREs for subsequent assembly of trans-complexes for fusion. A mutant of Sec17, with limited ability to stimulate Sec18, still strongly enhanced fusion when ample Sec18 was supplied, suggesting that Sec17 has additional functions. We used fusion reactions where the four SNAREs were initially separate, thus requiring no disassembly by Sec18. With proteoliposomes bearing asymmetrically disposed SNAREs, tethering and trans-SNARE pairing allowed slow fusion. Addition of Sec17 did not affect the levels of trans-SNARE complex but triggered sudden fusion of trans-SNARE paired proteoliposomes. …
Fungal Mediator Tail Subunits Contain Classical Transcriptional Activation Domains, Zhongle Liu, Lawrence C. Myers
Fungal Mediator Tail Subunits Contain Classical Transcriptional Activation Domains, Zhongle Liu, Lawrence C. Myers
Dartmouth Scholarship
Classical activation domains within DNA-bound eukaryotic transcription factors make weak interactions with coactivator complexes, such as Mediator, to stimulate transcription. How these interactions stimulate transcription, however, is unknown. The activation of reporter genes by artificial fusion of Mediator subunits to DNA binding domains that bind to their promoters has been cited as evidence that the primary role of activators is simply to recruit Mediator. We have identified potent classical transcriptional activation domains in the C termini of several tail module subunits of Saccharomyces cerevisiae, Candida albicans, and Candida dubliniensis Mediator, while their N-terminal domains are necessary and sufficient for their …
Med5(Nut1) And Med17(Srb4) Are Direct Targets Of Mediator Histone H4 Tail Interactions, Zhongle Liu, Lawrence C. Myers
Med5(Nut1) And Med17(Srb4) Are Direct Targets Of Mediator Histone H4 Tail Interactions, Zhongle Liu, Lawrence C. Myers
Dartmouth Scholarship
The Mediator complex transmits activation signals from DNA bound transcription factors to the core transcription machinery. In addition to its canonical role in transcriptional activation, recent studies have demonstrated that S. cerevisiae Mediator can interact directly with nucleosomes, and their histone tails. Mutations in Mediator subunits have shown that Mediator and certain chromatin structures mutually impact each other structurally and functionally in vivo. We have taken a UV photo cross-linking approach to further delineate the molecular basis of Mediator chromatin interactions and help determine whether the impact of certain Mediator mutants on chromatin is direct. Specifically, by using histone …
Mediator Influences Telomeric Silencing And Cellular Life Span, Xuefeng Zhu, Beidong Liu, Jonas O. P. Carlsten, Jenny Beve, Thomas Nyström, Lawrence C. Myers, Claes M. Gustafsson
Mediator Influences Telomeric Silencing And Cellular Life Span, Xuefeng Zhu, Beidong Liu, Jonas O. P. Carlsten, Jenny Beve, Thomas Nyström, Lawrence C. Myers, Claes M. Gustafsson
Dartmouth Scholarship
The Mediator complex is required for the regulated transcription of nearly all RNA polymerase II-dependent genes. Here we demonstrate a new role for Mediator which appears to be separate from its function as a transcriptional coactivator. Mediator associates directly with heterochromatin at telomeres and influences the exact boundary between active and inactive chromatin. Loss of the Mediator Med5 subunit or mutations in Med7 cause a depletion of the complex from regions located near subtelomeric X elements, which leads to a change in the balance between the Sir2 and Sas2 proteins. These changes in turn result in increased levels of H4K16 …
Minimal Membrane Docking Requirements Revealed By Reconstitution Of Rab Gtpase-Dependent Membrane Fusion From Purified Components, Christopher Stroupe, Christopher M. Hickey, Joji Mima, Amy S. Burfeind, William Wickner
Minimal Membrane Docking Requirements Revealed By Reconstitution Of Rab Gtpase-Dependent Membrane Fusion From Purified Components, Christopher Stroupe, Christopher M. Hickey, Joji Mima, Amy S. Burfeind, William Wickner
Dartmouth Scholarship
Rab GTPases and their effectors mediate docking, the initial contact of intracellular membranes preceding bilayer fusion. However, it has been unclear whether Rab proteins and effectors are sufficient for intermembrane interactions. We have recently reported reconstituted membrane fusion that requires yeast vacuolar SNAREs, lipids, and the homotypic fusion and vacuole protein sorting (HOPS)/class C Vps complex, an effector and guanine nucleotide exchange factor for the yeast vacuolar Rab GTPase Ypt7p. We now report reconstitution of lysis-free membrane fusion that requires purified GTP-bound Ypt7p, HOPS complex, vacuolar SNAREs, ATP hydrolysis, and the SNARE disassembly catalysts Sec17p and Sec18p. We use this …
Phosphoinositides And Snare Chaperones Synergistically Assemble And Remodel Snare Complexes For Membrane Fusion, Joji Mima, William Wickner
Phosphoinositides And Snare Chaperones Synergistically Assemble And Remodel Snare Complexes For Membrane Fusion, Joji Mima, William Wickner
Dartmouth Scholarship
Yeast vacuole fusion requires 4 SNAREs, 2 SNARE chaperone systems (Sec17p/Sec18p/ATP and the HOPS complex), and 2 phosphoinositides, phosphatidylinositol 3-phosphate [PI(3)P] and phosphatidylinositol 4,5-bisphosphate [PI(4,5)P2]. By reconstituting proteoliposomal fusion with purified components, we now show that phosphoinositides have 4 distinct roles: PI(3)P is recognized by the PX domain of the SNARE Vam7p; PI(3)P enhances the capacity of membrane-bound SNAREs to drive fusion in the absence of SNARE chaperones; either PI(3)P or PI(4,5)P2 can activate SNARE chaperones for the recruitment of Vam7p into fusion-competent SNARE complexes; and either PI(3)P or PI(4,5)P2 strikingly promotes synergistic SNARE complex remodeling …
Trans-Snare Complex Assembly And Yeast Vacuole Membrane Fusion, Kevin M. Collins, William T. Wickner
Trans-Snare Complex Assembly And Yeast Vacuole Membrane Fusion, Kevin M. Collins, William T. Wickner
Dartmouth Scholarship
cis-SNARE complexes (anchored in one membrane) are disassembled by Sec17p (α-SNAP) and Sec18p (NSF), permitting the unpaired SNAREs to assemble in trans. We now report a direct assay of trans-SNARE complex formation during yeast vacuole docking. SNARE complex assembly and fusion is promoted by high concentrations of the SNARE Vam7p or Nyv1p or by addition of HOPS (homotypic fusion and vacuole protein sorting), a Ypt7p (Rab)-effector complex with a Sec1/Munc18-family subunit. Inhibitors that target Ypt7p, HOPS, or key regulatory lipids prevent trans-SNARE complex assembly and ensuing fusion. Strikingly, the lipid ligand MED (myristoylated alanine-rich C kinase substrate effector domain) or …
Interdependent Assembly Of Specific Regulatory Lipids And Membrane Fusion Proteins Into The Vertex Ring Domain Of Docked Vacuoles, Rutilio A. Fratti, Youngsoo Jun, Alexey J. Merz, Nathan Margolis, William Wickner
Interdependent Assembly Of Specific Regulatory Lipids And Membrane Fusion Proteins Into The Vertex Ring Domain Of Docked Vacuoles, Rutilio A. Fratti, Youngsoo Jun, Alexey J. Merz, Nathan Margolis, William Wickner
Dartmouth Scholarship
Membrane microdomains are assembled by lipid partitioning (e.g., rafts) or by protein-protein interactions (e.g., coated vesicles). During docking, yeast vacuoles assemble "vertex" ring-shaped microdomains around the periphery of their apposed membranes. Vertices are selectively enriched in the Rab GTPase Ypt7p, the homotypic fusion and vacuole protein sorting complex (HOPS)-VpsC Rab effector complex, SNAREs, and actin. Membrane fusion initiates at vertex microdomains. We now find that the "regulatory lipids" ergosterol, diacylglycerol and 3- and 4-phosphoinositides accumulate at vertices in a mutually interdependent manner. Regulatory lipids are also required for the vertex enrichment of SNAREs, Ypt7p, and HOPS. Conversely, SNAREs and actin …
Trans-Snare Interactions Elicit Ca2+ Efflux From The Yeast Vacuole Lumen, Alexey J. Merz, William T. Wickner
Trans-Snare Interactions Elicit Ca2+ Efflux From The Yeast Vacuole Lumen, Alexey J. Merz, William T. Wickner
Dartmouth Scholarship
Ca2+ transients trigger many SNARE-dependent membrane fusion events. The homotypic fusion of yeast vacuoles occurs after a release of lumenal Ca2+. Here, we show that trans-SNARE interactions promote the release of Ca2+ from the vacuole lumen. Ypt7p-GTP, the Sec1p/Munc18-protein Vps33p, and Rho GTPases, all of which function during docking, are required for Ca2+ release. Inhibitors of SNARE function prevent Ca2+ release. Recombinant Vam7p, a soluble Q-SNARE, stimulates Ca2+ release. Vacuoles lacking either of two complementary SNAREs, Vam3p or Nyv1p, fail to release Ca2+ upon tethering. Mixing these two vacuole populations together allows Vam3p and Nyv1p to interact in trans and …
The Nuclear Pore Complex And The Dead Box Protein Rat8p/Dbp5p Have Nonessential Features Which Appear To Facilitate Mrna Export Following Heat Shock, Christiane Rollenhagen, Christine A. Hodge, Charles N. Cole
The Nuclear Pore Complex And The Dead Box Protein Rat8p/Dbp5p Have Nonessential Features Which Appear To Facilitate Mrna Export Following Heat Shock, Christiane Rollenhagen, Christine A. Hodge, Charles N. Cole
Dartmouth Scholarship
Nuclear pore complexes (NPCs) play an essential role in RNA export. Nucleoporins required for mRNA export in Saccharomyces cerevisiae are found in the Nup84p and Nup82p subcomplexes of the NPC. The Nup82p subcomplex contains Nup82p, Rat7p/Nup159p, Nsp1p, Gle1p/Rss1p, and Rip1p/Nup42p and is found only on the cytoplasmic face of NPCs. Both Rat7p and Gle1p contain binding sites for Rat8p/Dbp5p, an essential DEAD box protein and putative RNA helicase. Rip1p interacts directly with Gle1p and is the only protein known to be essential for mRNA export after heat shock but not under normal growth conditions. We report that in cells lacking …
Vam10p Defines A Sec18p-Independent Step Of Priming That Allows Yeast Vacuole Tethering, Masashi Kato, William Wickner
Vam10p Defines A Sec18p-Independent Step Of Priming That Allows Yeast Vacuole Tethering, Masashi Kato, William Wickner
Dartmouth Scholarship
YOR068c, termed VAM10 (altered vacuole morphology), lies within the VPS5 gene on the opposite DNA strand. VAM10 deletion causes vacuole fragmentation in vivo. The in vitro fusion of purified yeast vacuoles is stimulated by recombinant Vam10p and blocked by antibody to Vam10p. Vam10p acts early in the priming stage of fusion, independent of Sec18p. After priming, recombinant Vam10p will not stimulate fusion and anti-Vam10p antibodies will not inhibit; Vam10p provides a functional marker for this Sec18p-independent priming step. Pure Vam10p restores normal, Ypt7p-dependent tethering to vacuoles from a vam10Δ strain.
Remodeling Of Organelle-Bound Actin Is Required For Yeast Vacuole Fusion, Gary Eitzen, Li Wang, Naomi Thorngren, William Wickner
Remodeling Of Organelle-Bound Actin Is Required For Yeast Vacuole Fusion, Gary Eitzen, Li Wang, Naomi Thorngren, William Wickner
Dartmouth Scholarship
Actin participates in several intracellular trafficking pathways. We now find that actin, bound to the surface of purified yeast vacuoles in the absence of cytosol or cytoskeleton, regulates the last compartment mixing stage of homotypic vacuole fusion. The Cdc42p GTPase is known to be required for vacuole fusion. We now show that proteins of the Cdc42p-regulated actin remodeling cascade (Cdc42p --> Cla4p --> Las17p/Vrp1p --> Arp2/3 complex --> actin) are enriched on isolated vacuoles. Vacuole fusion is dramatically altered by perturbation of the vacuole-bound actin, either by mutation of the ACT1 gene, addition of specific actin ligands such as latrunculin …
A New Role For A Snare Protein As A Regulator Of The Ypt7/Rab-Dependent Stage Of Docking, Christian Ungermann, Albert Price, William Wickner
A New Role For A Snare Protein As A Regulator Of The Ypt7/Rab-Dependent Stage Of Docking, Christian Ungermann, Albert Price, William Wickner
Dartmouth Scholarship
The homotypic fusion of yeast vacuoles occurs in an ordered cascade of priming, docking, and fusion. The linkage between these steps has so far remained unclear. We now report that Vam7p (the vacuolar SNAP-23/25 homolog) signals from the cis-SNARE complex to Ypt7p (the vacuolar Rab/Ypt) to initiate the docking process. After Vam7p has been released from the cis-SNARE complex by Sec18p-mediated priming, it is still required for Ypt7p-dependent docking and it needs Ypt7p to remain on the vacuole.