title: Yeast phosphatidylinositol 4-kinase, Pik1, has essential roles at the Golgi and in the nucleus.
abstract: Phosphatidylinositol 4-kinase, Pik1, is essential for viability. GFP-Pik1 localized to cytoplasmic puncta and the nucleus. The puncta colocalized with Sec7-DsRed, a marker of trans-Golgi cisternae. Kap95 (importin-beta) was necessary for nuclear entry, but not Kap60 (importin-alpha), and exportin Msn5 was required for nuclear exit. Frq1 (frequenin orthologue) also is essential for viability and binds near the NH2 terminus of Pik1. Frq1-GFP localized to Golgi puncta, and Pik1 lacking its Frq1-binding site (or Pik1 overexpressed in frq1Delta cells) did not decorate the Golgi, but nuclear localization was unperturbed. Pik1(Delta10-192), which lacks its nuclear export sequence, displayed prominent nuclear accumulation and did not rescue inviability of pik1Delta cells. A Pik1-CCAAX chimera was excluded from the nucleus and also did not rescue inviability of pik1Delta cells. However, coexpression of Pik1(Delta10-192) and Pik1-CCAAX in pik1Delta cells restored viability. Catalytically inactive derivatives of these compartment-restricted Pik1 constructs indicated that PtdIns4P must be generated both in the nucleus and at the Golgi for normal cell function.
authors.affiliation: Department of Molecular and Cell Biology, University of California, Berkeley, Berkeley, CA 94720, USA.
authors.forename: Thomas
authors.initials: T
authors.lastname: Strahl
authors.forename: Hiroko
authors.initials: H
authors.lastname: Hama
authors.forename: Daryll B
authors.initials: DB
authors.lastname: DeWald
authors.forename: Jeremy
authors.initials: J
authors.lastname: Thorner
mesh_terms: D019870:1-Phosphatidylinositol 4-Kinase / Q000235:genetics / Q000502:physiology*; D021581:Active Transport, Cell Nucleus / Q000502:physiology; D002135:Calcium-Binding Proteins / Q000378:metabolism; D002467:Cell Nucleus / Q000378:metabolism*; D003600:Cytosol / Q000378:metabolism; D006056:Golgi Apparatus / Q000378:metabolism*; D049452:Green Fluorescent Proteins / Q000378:metabolism; D028884:Karyopherins / Q000378:metabolism; D008856:Microscopy, Fluorescence; D011994:Recombinant Proteins / Q000378:metabolism; D012441:Saccharomyces cerevisiae; D029701:Saccharomyces cerevisiae Proteins / Q000235:genetics / Q000378:metabolism / Q000502:physiology*
chemical_list: D002135:Calcium-Binding Proteins; C400903:FRQ1 protein, S cerevisiae; D028884:Karyopherins; C401306:MSN5 protein, S cerevisiae; D011994:Recombinant Proteins; D029701:Saccharomyces cerevisiae Proteins; D049452:Green Fluorescent Proteins; D019870:1-Phosphatidylinositol 4-Kinase; C441760:PIK1 protein, S cerevisiae