title: A protein containing a serine-rich domain with vesicle fusing properties mediates cell cycle-dependent cytosolic pH regulation.
abstract: Initial differentiation in Dictyostelium involves both asymmetric cell division and a cell cycle-dependent mechanism. We previously identified a gene, rtoA, which when disrupted randomizes the cell cycle-dependent mechanism without affecting either the underlying cell cycle or asymmetric differentiation. We find that in wild-type cells, RtoA levels vary during the cell cycle. Cytosolic pH, which normally varies with the cell cycle, is randomized in rtoA cells. The middle 60% of the RtoA protein is 10 tandem repeats of an 11 peptide-long serine-rich motif, which we find has a random coil structure. This domain catalyzes the fusion of phospholipid vesicles in vitro. Conversely, rtoA cells have a defect in the fusion of endocytic vesicles. They also have a decreased exocytosis rate, a decreased pH of endocytic/exocytic vesicles, and an increased average cytosolic pH. Our data indicate that the serine-rich domain of RtoA can mediate membrane fusion and that RtoA can increase the rate of vesicle fusion during processing of endoctyic vesicles. We hypothesize that RtoA modulates initial cell type choice by linking vegetative cell physiology to the cell cycle.
authors.affiliation: Howard Hughes Medical Institute and the Department of Biochemistry and Cell Biology, Rice University, Houston, Texas 77005-1892, USA.
authors.forename: D T
authors.initials: DT
authors.lastname: Brazill
authors.forename: D R
authors.initials: DR
authors.lastname: Caprette
authors.forename: H A
authors.initials: HA
authors.lastname: Myler
authors.forename: R D
authors.initials: RD
authors.lastname: Hatton
authors.forename: R R
authors.initials: RR
authors.lastname: Ammann
authors.forename: D F
authors.initials: DF
authors.lastname: Lindsey
authors.forename: D A
authors.initials: DA
authors.lastname: Brock
authors.forename: R H
authors.initials: RH
authors.lastname: Gomer
mesh_terms: D000818:Animals; D001483:Base Sequence; D002384:Catalysis; D002453:Cell Cycle; D018797:Cell Cycle Proteins / Q000737:chemistry / Q000378:metabolism*; D003600:Cytosol / Q000378:metabolism*; D017931:DNA Primers; D004023:Dictyostelium / Q000166:cytology / Q000378:metabolism*; D006863:Hydrogen-Ion Concentration; D008561:Membrane Fusion; D008854:Microscopy, Electron; D015388:Organelles / Q000378:metabolism; D015800:Protozoan Proteins / Q000737:chemistry / Q000378:metabolism*; D012694:Serine / Q000378:metabolism*
chemical_list: D018797:Cell Cycle Proteins; D017931:DNA Primers; D015800:Protozoan Proteins; C103074:RtoA protein, Dictyostelium discoideum; D012694:Serine