title: The spindle positioning protein Kar9p interacts with the sumoylation machinery in Saccharomyces cerevisiae.
abstract: Accurate positioning of the mitotic spindle is important for the genetic material to be distributed evenly in dividing cells, but little is known about the mechanisms that regulate this process. Here we report that two microtubule-associated proteins important for spindle positioning interact with several proteins in the sumoylation pathway. By two-hybrid analysis, Kar9p and Bim1p interact with the yeast SUMO Smt3p, the E2 enzyme Ubc9p, an E3 Nfi1p, as well as Wss1p, a weak suppressor of a temperature-sensitive smt3 allele. The physical interaction between Kar9p and Ubc9p was confirmed by in vitro binding assays. A single-amino-acid substitution in Kar9p, L304P disrupted its two-hybrid interaction with proteins in the sumoylation pathway, but retained its interactions with the spindle positioning proteins Bim1p, Stu2p, Bik1p, and Myo2p. The kar9-L304P mutant showed defects in positioning the mitotic spindle, with the spindle located more distally than normal. Whereas wild-type Kar9p-3GFP normally localizes to only the bud-directed spindle pole body (SPB), Kar9p-L304P-3GFP was mislocalized to both SPBs. Using a reconstitution assay, Kar9p was sumoylated in vitro. We propose a model in which sumoylation regulates spindle positioning by restricting Kar9p to one SPB. These findings raise the possibility that sumoylation could regulate other microtubule-dependent processes.
authors.affiliation: Department of Biochemistry and Molecular Biology, Oklahoma State University, Stillwater, Oklahoma 74078, USA.
authors.forename: Nida
authors.initials: N
authors.lastname: Meednu
authors.forename: Harold
authors.initials: H
authors.lastname: Hoops
authors.forename: Sonia
authors.initials: S
authors.lastname: D'Silva
authors.forename: Leah
authors.initials: L
authors.lastname: Pogorzala
authors.forename: Schuyler
authors.initials: S
authors.lastname: Wood
authors.forename: David
authors.initials: D
authors.lastname: Farkas
authors.forename: Mark
authors.initials: M
authors.lastname: Sorrentino
authors.forename: Elaine
authors.initials: E
authors.lastname: Sia
authors.forename: Pam
authors.initials: P
authors.lastname: Meluh
authors.forename: Rita K
authors.initials: RK
authors.lastname: Miller
mesh_terms: D001665:Binding Sites; D018797:Cell Cycle Proteins / Q000235:genetics / Q000378:metabolism; D008856:Microscopy, Fluorescence; D008868:Microtubule Proteins / Q000235:genetics / Q000378:metabolism; D009154:Mutation; D009687:Nuclear Proteins / Q000235:genetics / Q000378:metabolism*; D010766:Phosphorylation; D012097:Repressor Proteins / Q000235:genetics / Q000378:metabolism*; D012441:Saccharomyces cerevisiae / Q000378:metabolism*; D029701:Saccharomyces cerevisiae Proteins / Q000235:genetics / Q000378:metabolism*; D025841:Small Ubiquitin-Related Modifier Proteins / Q000235:genetics / Q000378:metabolism*; D008941:Spindle Apparatus / Q000378:metabolism*
chemical_list: C119683:BIM1 protein, S cerevisiae; D018797:Cell Cycle Proteins; C110443:KAR9 protein, S cerevisiae; D008868:Microtubule Proteins; D009687:Nuclear Proteins; D012097:Repressor Proteins; C099362:SMT3 protein, S cerevisiae; D029701:Saccharomyces cerevisiae Proteins; D025841:Small Ubiquitin-Related Modifier Proteins