title: A genetic screen for aminophospholipid transport mutants identifies the phosphatidylinositol 4-kinase, STT4p, as an essential component in phosphatidylserine metabolism.
abstract: In an effort to understand molecular mechanisms of intracellular lipid transport, we have focused upon specific events required for de novo aminophospholipid synthesis in the yeast Saccharomyces cerevisiae. A genetic system for examining the steps between phosphatidylserine (PtdSer) synthesis in the endoplasmic reticulum and its transport to and decarboxylation by PtdSer decarboxylase 2 in the Golgi/vacuole has been developed. We have isolated a mutant, denoted pstB1, that accumulates PtdSer and has diminished phosphatidylethanolamine formation despite normal PtdSer decarboxylase 2 activity. The lesion in PtdSer metabolism is consistent with a defect in interorganelle lipid transport. A genomic DNA clone that complements the mutation was isolated, and sequencing revealed that the clone contains the STT4 gene, encoding a phosphatidylinositol 4-kinase. The pstB1 mutant exhibits a defect in Stt4p-type phosphatidylinositol 4-kinase activity, and direct gene replacement indicates that STT4 is the defective gene in the mutant. Creation of an STT4 null allele (stt4Delta::HIS3) demonstrates the gene is essential. These results provide evidence that implicates phosphoinositides in the regulation of intracellular aminophospholipid transport.
authors.affiliation: Division of Nutritional Sciences and Institute for Cellular and Molecular Biology, The University of Texas, Austin, Texas 78712, USA.
authors.forename: P J
authors.initials: PJ
authors.lastname: Trotter
authors.forename: W I
authors.initials: WI
authors.lastname: Wu
authors.forename: J
authors.initials: J
authors.lastname: Pedretti
authors.forename: R
authors.initials: R
authors.lastname: Yates
authors.forename: D R
authors.initials: DR
authors.lastname: Voelker
mesh_terms: D019870:1-Phosphatidylinositol 4-Kinase / Q000235:genetics / Q000378:metabolism*; D001692:Biological Transport; D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism*; D005816:Genetic Complementation Test; D016296:Mutagenesis; D010718:Phosphatidylserines / Q000096:biosynthesis / Q000378:metabolism*; D012441:Saccharomyces cerevisiae / Q000201:enzymology / Q000378:metabolism; D029701:Saccharomyces cerevisiae Proteins; D013347:Subcellular Fractions / Q000201:enzymology / Q000378:metabolism
chemical_list: D002352:Carrier Proteins; D010718:Phosphatidylserines; D029701:Saccharomyces cerevisiae Proteins; D019870:1-Phosphatidylinositol 4-Kinase; C441760:PIK1 protein, S cerevisiae