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Spindle Checkpoint Maintenance Requires Ame1 and Okp1
Isabelle Pot, James Knockleby, Victoria Aneliunas, Thao Nguyen, Sonia Ah-Kye, Gregory Liszt, Michael Snyder, Philip Hieter and Jackie Vogel
volume 4 | issue 10
october 2005Pages: 1448 - 1456
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Kinetochore proteins are required for high fidelity chromosome segregation and as a platform for checkpoint signaling. Ame1 is an essential component of the COMA (Ctf19, Okp1, Mcm21, Ame1) sub-complex of the central kinetochore of budding yeast. In this study, we describe the isolation and characterization of an Ame1 conditional mutant, ame1-4. ame1-4 cells exhibit chromosome segregation defects and Mad2-dependent cell cycle delay similar to okp1-5 cells. However, the viability of ame1-4 cells is markedly reduced relative to wild type and okp1-5 cells after 3 hours at restrictive temperature. To determine if ame1-4 cells enter anaphase with mis-segregated chromosomes, we monitored the localization of Bub3:VFP as a marker for anaphase onset. ame1-4 cells containing mis-segregated sister chromatids initially accumulate Bub3:VFP at kinetochores, indicating checkpoint activation and a metaphase arrest. Subsequently, Bub3:VFP de-localizes and cells re-initiate DNA duplication and budding without cytokinesis in the presence of un-segregated chromosomes. Over-expression of OKP1 in ame1-4 cells restores ame1-4 protein localization and a stable arrest. Based on our results, we propose that Ame1 and Okp1 are required for a sustained checkpoint arrest in the presence of mis-segregated chromosomes. Our results suggest that checkpoint response might be controlled not only at the level of activation but also via signals that ensure maintenance of the response.
We now provide open access to journal articles published online for one year or more. This article may be downloaded at the following link:
Download PDF If the document does not open, please right-click on the link (control-click on a Macintosh) and select the option to save the file to disk.