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Phosphorylation of the chromosomal passenger protein Bir1 is required for localization of Ndc10 to the spindle during anaphase and full spindle elongation.

The Saccharomyces cerevisiae inhibitor of apoptosis (IAP) repeat protein Bir1 localizes as a chromosomal passenger. A deletion analysis of Bir1 identified two regions important for function. The C-terminal region is essential for growth, binds Sli15, and is necessary and sufficient for the localization of Bir1 as a chromosomal passenger. The middle region is not essential but is required to localize the inner kinetochore protein Ndc10 to the spindle during anaphase and to the midzone at telophase. In contrast, precise deletion of the highly conserved IAP repeats conferred no phenotype and did not alter the cell cycle delay caused by loss of cohesin. Bir1 is phosphorylated in a cell cycle-dependent manner. Mutation of all nine CDK consensus sites in the middle region of Bir1 significantly decreased the level of phosphorylation and blocked localization of Ndc10 to the spindle at anaphase. Moreover, immunoprecipitation of Ndc10 with Bir1 was dependent on phosphorylation. The loss of Ndc10 from the anaphase spindle prevented elongation of the spindle beyond 7 microm. We conclude that phosphorylation of the middle region of Bir1 is required to bring Ndc10 to the spindle at anaphase, which is required for full spindle elongation.

Pubmed ID: 16381814


  • Widlund PO
  • Lyssand JS
  • Anderson S
  • Niessen S
  • Yates JR
  • Davis TN


Molecular biology of the cell

Publication Data

March 27, 2006

Associated Grants

  • Agency: NCRR NIH HHS, Id: P41 RR-01823
  • Agency: NCRR NIH HHS, Id: P41 RR011823
  • Agency: NIGMS NIH HHS, Id: R01 GM-40506
  • Agency: NIGMS NIH HHS, Id: T32 GM-07270

Mesh Terms

  • Anaphase
  • Chromosome Deletion
  • Chromosomes, Fungal
  • DNA-Binding Proteins
  • Fungal Proteins
  • Gene Deletion
  • Inhibitor of Apoptosis Proteins
  • Kinetochores
  • Microtubule-Associated Proteins
  • Phosphorylation
  • Protein Binding
  • Protein Transport
  • Saccharomyces cerevisiae
  • Saccharomyces cerevisiae Proteins
  • Spindle Apparatus