title: Inositol hexakisphosphate and Gle1 activate the DEAD-box protein Dbp5 for nuclear mRNA export.
abstract: Regulation of nuclear mRNA export is critical for proper eukaryotic gene expression. A key step in this process is the directional translocation of mRNA-ribonucleoprotein particles (mRNPs) through nuclear pore complexes (NPCs) that are embedded in the nuclear envelope. Our previous studies in Saccharomyces cerevisiae defined an in vivo role for inositol hexakisphosphate (InsP6) and NPC-associated Gle1 in mRNA export. Here, we show that Gle1 and InsP6 act together to stimulate the RNA-dependent ATPase activity of the essential DEAD-box protein Dbp5. Overexpression of DBP5 specifically suppressed mRNA export and growth defects of an ipk1 nup42 mutant defective in InsP6 production and Gle1 localization. In vitro kinetic analysis showed that InsP6 significantly increased Dbp5 ATPase activity in a Gle1-dependent manner and lowered the effective RNA concentration for half-maximal ATPase activity. Gle1 alone had minimal effects. Maximal InsP6 binding required both Dbp5 and Gle1. It has been suggested that Dbp5 requires unidentified cofactors. We now propose that Dbp5 activation at NPCs requires Gle1 and InsP6. This would facilitate spatial control of the remodelling of mRNP protein composition during directional transport and provide energy to power transport cycles.
authors.affiliation: Department of Cell and Developmental Biology, Vanderbilt University Medical Center, U-3209 MRBIII, 465 21st Avenue South, Nashville, TN 37232-8240, USA.
authors.forename: Abel R
authors.initials: AR
authors.lastname: Alcázar-Román
authors.forename: Elizabeth J
authors.initials: EJ
authors.lastname: Tran
authors.forename: Shuangli
authors.initials: S
authors.lastname: Guo
authors.forename: Susan R
authors.initials: SR
authors.lastname: Wente
mesh_terms: D021581:Active Transport, Cell Nucleus / Q000502:physiology; D001665:Binding Sites / Q000502:physiology; D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism*; D053487:DEAD-box RNA Helicases; D004789:Enzyme Activation / Q000502:physiology; D022022:Nuclear Pore / Q000378:metabolism* / Q000648:ultrastructure; D028861:Nuclear Pore Complex Proteins; D029543:Nucleocytoplasmic Transport Proteins / Q000235:genetics / Q000378:metabolism*; D010833:Phytic Acid / Q000378:metabolism*; D020365:RNA Helicases / Q000235:genetics / Q000378:metabolism*; D012333:RNA, Messenger / Q000378:metabolism*; D012261:Ribonucleoproteins / Q000378:metabolism; D012441:Saccharomyces cerevisiae / Q000235:genetics / Q000378:metabolism*; D029701:Saccharomyces cerevisiae Proteins / Q000235:genetics / Q000378:metabolism*; D015854:Up-Regulation / Q000502:physiology
chemical_list: D002352:Carrier Proteins; C101408:GLE1 protein, S cerevisiae; D028861:Nuclear Pore Complex Proteins; D029543:Nucleocytoplasmic Transport Proteins; D012333:RNA, Messenger; D012261:Ribonucleoproteins; D029701:Saccharomyces cerevisiae Proteins; C026452:messenger ribonucleoprotein; D010833:Phytic Acid; C492382:DBP5 protein, S cerevisiae; D053487:DEAD-box RNA Helicases; D020365:RNA Helicases