Abstract
The kinetochore is a large, evolutionarily conserved protein structure that connects chromosomes with microtubules. During chromosome segregation, outer kinetochore components track depolymerizing ends of microtubules to facilitate the separation of chromosomes into two cells. In budding yeast, each chromosome has a point centromere upon which a single kinetochore is built, which attaches to a single microtubule. This defined architecture facilitates quantitative examination of kinetochores during the cell cycle. Using three independent measures-calibrated imaging, FRAP, and photoconversion-we find that the Dam1 submodule is unchanged during anaphase, whereas MIND and Ndc80 submodules add copies to form an "anaphase configuration" kinetochore. Microtubule depolymerization and kinesin-related motors contribute to copy addition. Mathematical simulations indicate that the addition of microtubule attachments could facilitate tracking during rapid microtubule depolymerization. We speculate that the minimal kinetochore configuration, which exists from G1 through metaphase, allows for correction of misattachments. Our study provides insight into dynamics and plasticity of the kinetochore structure during chromosome segregation in living cells.
Highlights
Pairs of sister chromatids must be precisely divided into two cells during cell division to prevent missegregation
Cells having no bud were categorized as G1 phase, whereas anaphase cells exhibited the maximum distance between kinetochore clusters or spindle pole bodies (SPBs)
Experiments using purified yeast kinetochores have revealed that microtubule depolymerization makes kinetochores highly susceptible to detachment (Akiyoshi et al, 2010), which in turn could be deleterious for chromosome transmission
Summary
Pairs of sister chromatids must be precisely divided into two cells during cell division to prevent missegregation. Understanding the mechanisms of chromosome segregation is critical to understanding the fidelity of chromosome transmission. Microtubules attach to the chromosome via kinetochores and pull them to the poles during chromosome segregation. The kinetochore is a several-megadalton–sized protein structure assembled on a specialized region of the chromosome called the centromere. The centromeric region is a ∼130-bp sequence in budding yeast and is epigenetically defined in higher organisms. Each kinetochore interacts with multiple microtubules (McAinsh et al, 2003; Chan et al, 2005; Walczak et al, 2010), whereas in Saccharomyces cerevisiae, each chromosome interacts with only one microtubule (Winey et al, 1995), making it an ideal defined system for studying kinetochore–microtubule interaction
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