title: A Rab requirement is not bypassed in SLY1-20 suppression.
abstract: The Rab GTPase Ypt1p and the large homodimer Uso1p are both required for tethering endoplasmic reticulum-derived vesicles to early Golgi compartments in yeast. Loss-of-function ypt1 and uso1 mutations are suppressed by SLY1-20, a dominant allele that encodes the Sed5p-associated protein, Sly1p. Here, we investigate the mechanism of SLY1-20 suppression. In wild-type strains, Ypt1p can be coimmunoprecipitated with Uso1p; however, in a ypt1Delta/SLY1-20 strain, which lacks this complex, membrane binding of Uso1p was reduced. In spite of Ypt1p depletion, Uso1p-dependent vesicle tethering was not bypassed under the ypt1Delta/SLY1-20 condition. Moreover, tethering and fusion assays with ypt1Delta/SLY1-20 membranes remained sensitive to Rab GDP dissociation inhibitor. These results indicate that an alternative Rab protein satisfies the Ypt1p requirement in Uso1p-dependent tethering when SLY1-20 is expressed. Further genetic and biochemical tests revealed that a related Rab protein, Ypt6, might substitute for Ypt1p in ypt1Delta/SLY1-20 cells. Additional experimentation to address the mechanism of SLY1-20 suppression in a cog2Delta [sec35Delta] strain indicated that the Cog2p subunit of the conserved oligomeric Golgi complex is either functionally redundant or is not directly required for anterograde transport to the Golgi complex.
authors.affiliation: Department of Biochemistry, Dartmouth Medical School, Hanover, NH 03755, USA.
authors.forename: Nicole
authors.initials: N
authors.lastname: Ballew
authors.forename: Yiting
authors.initials: Y
authors.lastname: Liu
authors.forename: Charles
authors.initials: C
authors.lastname: Barlowe
mesh_terms: D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism*; D002462:Cell Membrane / Q000378:metabolism; D015966:Gene Expression Regulation, Fungal; D020730:Guanine Nucleotide Dissociation Inhibitors / Q000235:genetics / Q000378:metabolism; D047468:Immunoprecipitation; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism; D051938:Munc18 Proteins; D011485:Protein Binding; D021381:Protein Transport; D012441:Saccharomyces cerevisiae / Q000166:cytology / Q000235:genetics / Q000378:metabolism*; D029701:Saccharomyces cerevisiae Proteins / Q000235:genetics / Q000378:metabolism*; D013489:Suppression, Genetic / Q000235:genetics*; D015854:Up-Regulation; D033921:Vesicular Transport Proteins / Q000235:genetics / Q000378:metabolism; D020691:rab GTP-Binding Proteins / Q000172:deficiency / Q000235:genetics / Q000378:metabolism*
chemical_list: C112749:COG2 protein, S cerevisiae; D002352:Carrier Proteins; D020730:Guanine Nucleotide Dissociation Inhibitors; D008565:Membrane Proteins; D051938:Munc18 Proteins; C072520:SLY1 protein, S cerevisiae; D029701:Saccharomyces cerevisiae Proteins; C086888:USO1 protein, S cerevisiae; D033921:Vesicular Transport Proteins; C060755:YPT1 protein, S cerevisiae; D020691:rab GTP-Binding Proteins