title: Interaction of Pik1p and Sjl proteins in membrane trafficking.
abstract: Phosphatidylinositol (PtdIns) phosphates are involved in signal transduction, cytoskeletal organization, and membrane traffic. PtdIns 4-phosphate [PtdIns(4)P], produced in yeast by PtdIns 4-kinase (Pik1p), appears to regulate Golgi secretory function. PtdIns(4)P is also produced by dephosphorylation of phosphatidylinositol 4,5-bisphosphate [PtdIns(4,5)P2], catalyzed by one of the three yeast Sjl proteins, homologs of the mammalian synaptic vesicle-associated PtdIns(4,5)P2 5-phosphatase, synaptojanin. To determine whether Pik1p and Sjl proteins operate in the same pathway or regulate the same process, we used a genetic approach. Mutation in the PIK1 gene displays synthetic genetic interactions with deletions of individual SJL genes. Deletion of SJL3 gene is synthetically lethal with pik1ts, and deletions of SJL1 or SJL2 genes in pik1ts cells exacerbate the temperature sensitivity, neomycin sensitivity, and defect in invertase secretion. A diminished level of PtdIns(4)P and increased level of PtdIns(4,5)P2 in pik1(ts)sjl1delta and pik1(ts)sjl2delta cells, compared with pik1ts cells, indicate that PtdIns(4)P is specifically required for secretion. Collectively, our results suggest that Pik1p and the Sjl proteins coordinately function to regulate the dynamic phosphorylation-dephosphorylation of the polar heads of phosphoinositides, and this process appears to be important for membrane trafficking pathways.
authors.affiliation: Department of Biological Sciences, St. John's University, 8000 Utopia Parkway, Jamaica, NY 11439, USA.
authors.forename: Peter H
authors.initials: PH
authors.lastname: Nguyen
authors.forename: Jiri
authors.initials: J
authors.lastname: Hasek
authors.forename: Sepp D
authors.initials: SD
authors.lastname: Kohlwein
authors.forename: Carlos
authors.initials: C
authors.lastname: Romero
authors.forename: Jae H
authors.initials: JH
authors.lastname: Choi
authors.forename: Ales
authors.initials: A
authors.lastname: Vancura
mesh_terms: D019870:1-Phosphatidylinositol 4-Kinase / Q000235:genetics / Q000378:metabolism*; D002462:Cell Membrane / Q000378:metabolism*; D017353:Gene Deletion; D015966:Gene Expression Regulation, Fungal; D018129:Phosphatidylinositol Phosphates / Q000378:metabolism; D010744:Phosphoric Monoester Hydrolases / Q000235:genetics / Q000378:metabolism*; D010766:Phosphorylation; D012441:Saccharomyces cerevisiae / Q000201:enzymology* / Q000235:genetics; D029701:Saccharomyces cerevisiae Proteins / Q000235:genetics / Q000378:metabolism
chemical_list: D018129:Phosphatidylinositol Phosphates; D029701:Saccharomyces cerevisiae Proteins; D019870:1-Phosphatidylinositol 4-Kinase; C110551:INP51 protein, S cerevisiae; D010744:Phosphoric Monoester Hydrolases