Loss of Function of the Cik1/Kar3 Motor Complex Results in Chromosomes with Syntelic Attachment That Are Sensed by the Tension Checkpoint

The University of North Carolina at Chapel Hill, United States of America
PLoS Genetics (Impact Factor: 7.53). 02/2012; 8(2):e1002492. DOI: 10.1371/journal.pgen.1002492
Source: PubMed


The attachment of sister kinetochores by microtubules emanating from opposite spindle poles establishes chromosome bipolar attachment, which generates tension on chromosomes and is essential for sister-chromatid segregation. Syntelic attachment occurs when both sister kinetochores are attached by microtubules from the same spindle pole and this attachment is unable to generate tension on chromosomes, but a reliable method to induce syntelic attachments is not available in budding yeast. The spindle checkpoint can sense the lack of tension on chromosomes as well as detached kinetochores to prevent anaphase onset. In budding yeast Saccharomyces cerevisiae, tension checkpoint proteins Aurora/Ipl1 kinase and centromere-localized Sgo1 are required to sense the absence of tension but are dispensable for the checkpoint response to detached kinetochores. We have found that the loss of function of a motor protein complex Cik1/Kar3 in budding yeast leads to syntelic attachments. Inactivation of either the spindle or tension checkpoint enables premature anaphase entry in cells with dysfunctional Cik1/Kar3, resulting in co-segregation of sister chromatids. Moreover, the abolished Kar3-kinetochore interaction in cik1 mutants suggests that the Cik1/Kar3 complex mediates chromosome movement along microtubules, which could facilitate bipolar attachment. Therefore, we can induce syntelic attachments in budding yeast by inactivating the Cik1/Kar3 complex, and this approach will be very useful to study the checkpoint response to syntelic attachments.

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    • "We deleted the FIN1 and BMH1 genes with a Sphis5 + marker as described previously (Longtine et al., 1998), and the resulting deletion mutants were confirmed using PCR. Yeast cell growth, synchronization , and CIK1-CC overexpression were performed as described previously (Jin et al., 2012). "
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    • "The delay of chromosome bipolar attachment in slk19Δ cells could increase the chance of syntelic attachments, in which both sister kinetochores are connected to microtubules emanating from a single spindle pole. Sgo1 is a component of the tension checkpoint that senses syntelic attachment and delays anaphase onset (Indjeian et al., 2005; Jin et al., 2012). If syntelic attachments occur in slk19Δ cells after nocodazole treatment, these cells will show a Sgo1-dependent cell cycle delay. "
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