Asymmetric loading of Kar9 onto spindle poles and microtubules ensures proper spindle alignment

Cell. 2003 Feb 21;112(4):561-74. doi: 10.1016/s0092-8674(03)00119-3.


Spindle alignment is the process in which the two spindle poles are directed toward preselected and opposite cell ends. In budding yeast, the APC-related molecule Kar9 is required for proper alignment of the spindle with the mother-bud axis. We find that Kar9 localizes to the prospective daughter cell spindle pole. Kar9 is transferred from the pole to cytoplasmic microtubules, which are then guided in a myosin-dependent manner to the bud. Clb4/Cdc28 kinase phosphorylates Kar9 and accumulates on the pole destined to the mother cell. Mutations that block phosphorylation at Cdc28 consensus sites result in localization of Kar9 to both poles and target them both to the bud. Thus, Clb4/Cdc28 prevents Kar9 loading on the mother bound pole. In turn, asymmetric distribution of Kar9 ensures that only one pole orients toward the bud. Our results indicate that Cdk1-dependent spindle asymmetry ensures proper alignment of the mitotic spindle with the cell division axis.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Actins / metabolism
  • Alleles
  • Amino Acid Sequence
  • Animals
  • CDC28 Protein Kinase, S cerevisiae / metabolism
  • Cell Cycle Proteins / metabolism
  • Cell Division
  • Cell Movement
  • Cyclin B
  • Cyclins / metabolism
  • Cytoplasm / metabolism
  • Green Fluorescent Proteins
  • Luminescent Proteins / metabolism
  • Microscopy, Fluorescence
  • Microscopy, Video
  • Microtubules / metabolism
  • Microtubules / ultrastructure*
  • Mitosis
  • Models, Biological
  • Molecular Sequence Data
  • Mutation
  • Myosin Heavy Chains / metabolism
  • Myosin Type V / metabolism
  • Nuclear Proteins / metabolism*
  • Phosphorylation
  • Plasmids / metabolism
  • Saccharomyces cerevisiae Proteins / metabolism
  • Saccharomycetales / physiology
  • Sequence Homology, Amino Acid
  • Spindle Apparatus / physiology*
  • Temperature
  • Time Factors


  • Actins
  • CLB4 protein, S cerevisiae
  • Cell Cycle Proteins
  • Cyclin B
  • Cyclins
  • KAR9 protein, S cerevisiae
  • Luminescent Proteins
  • MYO2 protein, S cerevisiae
  • Nuclear Proteins
  • Saccharomyces cerevisiae Proteins
  • Green Fluorescent Proteins
  • CDC28 Protein Kinase, S cerevisiae
  • Myosin Type V
  • Myosin Heavy Chains