title: SEC14-dependent secretion in Saccharomyces cerevisiae. Nondependence on sphingolipid synthesis-coupled diacylglycerol production.
abstract: The SEC14 gene in Saccharomyces cerevisiae encodes a phosphatidylinositol transfer protein required for secretory protein movement from the Golgi. Mutation of SAC1, a gene of unknown function, restores secretory flow in sec14-1(ts) strains. The existing model for the bypass of the sec14-1(ts) defect by sac1-22 involves stimulation of sphingolipid biosynthesis and, in particular, the synthesis of mannosyl-diinositolphosphoryl-ceramide with concomitant increases in Golgi diacylglycerol levels. To test this model, we disrupted IPT1, the mannosyl-diinositolphosphoryl-ceramide synthase of S. cerevisiae. Disruption of the IPT1 gene had no effect on the ability of sac1-22 to bypass sec14-1(ts). Furthermore, sphingolipid analysis of sec14-1(ts) and sec14-1(ts) sac1-22 strains showed that mannosyl-diinositolphosphoryl-ceramide synthesis was not stimulated in the bypass mutant. However, the sec14-1(ts) strain had elevated mannosyl-monoinositolphosphoryl-ceramide levels, and the sec14-1(ts) sac1-22 strain showed an 8-fold increase in phosphatidylinositol 4-phosphate along with a decrease in phosphatidylinositol 4,5-bisphosphate. Cellular diacylglycerol levels, measured by [14C]acetate incorporation, did not differ between the sec14-1(ts) and the sec14-1 sac1-22 bypass strains, although disruption of IPT1 in the bypass strain resulted in reduced levels. These data indicate that phosphatidylinositol 4-phosphate, rather than mannosyl-diinositolphosphoryl-ceramide, accumulates in the sec14-1(ts) sac1-22 bypass strain, and that Golgi diacylglycerol accumulation is not required for bypass of the sec14-1(ts) growth and secretory phenotypes.
authors.affiliation: Department of Biology, Utah State University, Logan, Utah 84322-5305, USA.
authors.forename: S D
authors.initials: SD
authors.lastname: Stock
authors.forename: H
authors.initials: H
authors.lastname: Hama
authors.forename: D B
authors.initials: DB
authors.lastname: DeWald
authors.forename: J Y
authors.initials: JY
authors.lastname: Takemoto
mesh_terms: D002352:Carrier Proteins / Q000378:metabolism*; D004075:Diglycerides / Q000096:biosynthesis*; D008565:Membrane Proteins; D009154:Mutation; D018129:Phosphatidylinositol Phosphates / Q000378:metabolism; D049294:Phospholipid Transfer Proteins; D017853:Phosphotransferases (Alcohol Group Acceptor) / Q000235:genetics; D012441:Saccharomyces cerevisiae / Q000235:genetics* / Q000378:metabolism; D029701:Saccharomyces cerevisiae Proteins; D013107:Sphingolipids / Q000096:biosynthesis* / Q000378:metabolism
chemical_list: D002352:Carrier Proteins; D004075:Diglycerides; D008565:Membrane Proteins; D018129:Phosphatidylinositol Phosphates; D049294:Phospholipid Transfer Proteins; C483438:SEC14 protein, S cerevisiae; C118289:SEC24 protein, S cerevisiae; D029701:Saccharomyces cerevisiae Proteins; D013107:Sphingolipids; C037178:phosphatidylinositol 4-phosphate; C109311:IPT1 protein, S cerevisiae; D017853:Phosphotransferases (Alcohol Group Acceptor)