Phosphorylation of the Chromosomal Passenger Protein Bir1 Is Required for Localization of Ndc10 to the Spindle during Anaphase and Full Spindle Elongation

Department of Biochemistry, University of Washington, Seattle, WA 98195-7350, USA.
Molecular Biology of the Cell (Impact Factor: 4.47). 04/2006; 17(3):1065-74. DOI: 10.1091/mbc.E05-07-0640
Source: PubMed


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.

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    • "The cleavage of Mcd1 under oxidative stress suggests the interruption or mis-regulation of the spindle assembly checkpoint, which regulates the APC activation. Bir1 is a chromosomal passenger protein involved in coordinating cell cycle events for proper chromosome segregation (Widlund et al., 2006). It has been shown that Bir1 is required for recruiting condensin. "
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    • "Ndc10 is released in a Cdc14-dependent fashion from the kinetochore to microtubule plus ends where it contributes to spindle stability specifically in anaphase (Bouck and Bloom 2005). Ndc10 is critical for spindle elongation to the full 10–12 mm prior to spindle disassembly and cytokinesis (Widlund et al. 2006). Additional substrates have recently been identified in studies directed at exploring this critical aspect of spindle morphogenesis (Vizeacoumar et al. 2010; Woodruff et al. 2010). "
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    • "Consistently, our study showed that Ndc10(4D), a constitutively phosphorylated Ndc10, failed to target to anaphase spindles. Localization of Ndc10 to the spindle depends on Ndc10 binding to Bir1, an essential component of the CPC, and the Ndc10-Bir1 interaction is subject to regulation of Cdk1 phosphorylation (Widlund et al., 2006). In addition to regulation of Ndc10 targeting to spindles by Ipl1, Ndc10 is also sumoylated, and its sumoylation is required for its binding to Bir1 and hence Ndc10 spindle localization (Montpetit et al., 2006). "
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