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      Mitochondrial Fusion in Yeast Requires the Transmembrane GTPase Fzo1p


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          Membrane fusion is required to establish the morphology and cellular distribution of the mitochondrial compartment. In Drosophila, mutations in the fuzzy onions ( fzo) GTPase block a developmentally regulated mitochondrial fusion event during spermatogenesis. Here we report that the yeast orthologue of fuzzy onions, Fzo1p, plays a direct and conserved role in mitochondrial fusion. A conditional fzo1 mutation causes the mitochondrial reticulum to fragment and blocks mitochondrial fusion during yeast mating. Fzo1p is a mitochondrial integral membrane protein with its GTPase domain exposed to the cytoplasm. Point mutations that alter conserved residues in the GTPase domain do not affect Fzo1p localization but disrupt mitochondrial fusion. Suborganellar fractionation suggests that Fzo1p spans the outer and is tightly associated with the inner mitochondrial membrane. This topology may be required to coordinate the behavior of the two mitochondrial membranes during the fusion reaction. We propose that the fuzzy onions family of transmembrane GTPases act as molecular switches to regulate a key step in mitochondrial membrane docking and/or fusion.

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          Construction of a set of convenient Saccharomyces cerevisiae strains that are isogenic to S288C.

          A set of GAL2+ yeast strains that are isogenic to strain S288C have been constructed. They contain non-reverting mutations in genes commonly used for selection for recombinant plasmids. Strains from this collection are being used for the European Union Yeast Genome Sequencing Programme. Representative strains from this collection have been deposited with the ATCC.
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            Regulatable promoters of Saccharomyces cerevisiae: comparison of transcriptional activity and their use for heterologous expression.

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              Mammalian Ras interacts directly with the serine/threonine kinase Raf.

              We have identified proteins that interact with H-Ras using a two hybrid system screen of a mouse cDNA library. Approximately 50% of the clones identified encoded portions of the c-Raf and A-Raf serine/threonine kinases. Overlaps among these clones define a conserved 81 residue region of the N-terminus of Raf as the Ras interaction region. We show that Raf interacts with wild-type and activated Ras, but not with an effector domain mutant of Ras or with a dominant-interfering Ras mutant. Using purified bacterially expressed fusion proteins, we show, furthermore, that Ras and the N-terminal region of Raf associate directly in vitro and that this interaction is dependent on GTP bound to Ras.

                Author and article information

                J Cell Biol
                The Journal of Cell Biology
                The Rockefeller University Press
                19 October 1998
                : 143
                : 2
                : 359-373
                [* ]Department of Biology, University of Utah, Salt Lake City, Utah 84112; []Department of Developmental Biology and Department of Genetics, Stanford University School of Medicine, Stanford, California 94305; and [§ ]Department of Molecular and Cellular Biology, University of California, Davis, California 95616
                Copyright @ 1998
                : 4 August 1998
                : 25 August 1998
                Regular Articles

                Cell biology
                gtpase,membrane fusion,mitochondria,mtdna,organelle morphology
                Cell biology
                gtpase, membrane fusion, mitochondria, mtdna, organelle morphology


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