title: The dynamin-like GTPase Sey1p mediates homotypic ER fusion in S. cerevisiae.
abstract: The endoplasmic reticulum (ER) forms a network of tubules and sheets that requires homotypic membrane fusion to be maintained. In metazoans, this process is mediated by dynamin-like guanosine triphosphatases (GTPases) called atlastins (ATLs), which are also required to maintain ER morphology. Previous work suggested that the dynamin-like GTPase Sey1p was needed to maintain ER morphology in Saccharomyces cerevisiae. In this paper, we demonstrate that Sey1p, like ATLs, mediates homotypic ER fusion. The absence of Sey1p resulted in the ER undergoing delayed fusion in vivo and proteoliposomes containing purified Sey1p fused in a GTP-dependent manner in vitro. Sey1p could be partially replaced by ATL1 in vivo. Like ATL1, Sey1p underwent GTP-dependent dimerization. We found that the residual ER-ER fusion that occurred in cells lacking Sey1p required the ER SNARE Ufe1p. Collectively, our results show that Sey1p and its homologues function analogously to ATLs in mediating ER fusion. They also indicate that S. cerevisiae has an alternative fusion mechanism that requires ER SNAREs.
authors.affiliation: Laboratory of Molecular and Cell Biology, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, MD 20892, USA.
authors.forename: Kamran
authors.initials: K
authors.lastname: Anwar
authors.forename: Robin W
authors.initials: RW
authors.lastname: Klemm
authors.forename: Amanda
authors.initials: A
authors.lastname: Condon
authors.forename: Katharina N
authors.initials: KN
authors.lastname: Severin
authors.forename: Miao
authors.initials: M
authors.lastname: Zhang
authors.forename: Rodolfo
authors.initials: R
authors.lastname: Ghirlando
authors.forename: Junjie
authors.initials: J
authors.lastname: Hu
authors.forename: Tom A
authors.initials: TA
authors.lastname: Rapoport
authors.forename: William A
authors.initials: WA
authors.lastname: Prinz
mesh_terms: D004721:Endoplasmic Reticulum / Q000378:metabolism* / Q000648:ultrastructure; D019204:GTP-Binding Proteins / Q000378:metabolism; D055786:Gene Knockout Techniques; D008561:Membrane Fusion / Q000502:physiology*; D008565:Membrane Proteins / Q000378:metabolism; D050765:Qa-SNARE Proteins / Q000378:metabolism; D012441:Saccharomyces cerevisiae / Q000378:metabolism* / Q000648:ultrastructure; D029701:Saccharomyces cerevisiae Proteins / Q000235:genetics* / Q000378:metabolism*; D033921:Vesicular Transport Proteins / Q000235:genetics* / Q000378:metabolism*
chemical_list: D008565:Membrane Proteins; D050765:Qa-SNARE Proteins; C472231:SEY1 protein, S cerevisiae; D029701:Saccharomyces cerevisiae Proteins; C103868:UFE1 protein, S cerevisiae; D033921:Vesicular Transport Proteins; C440006:ATL1 protein, human; D019204:GTP-Binding Proteins