Biology subjects

Hedouin, S.

Publications and source records attributed to Hedouin, S..

3 recordsLinked to original sources

bioRxiv2026

Native yeast kinetochore structures identify an essential inner kinetochore interaction

Kinetochores must accurately assemble on centromeres for faithful chromosome segregation. Although a conserved centromeric nucleosome is essential for kinetochore assembly, budding yeast centromeric DNA is a poor template for nucleosome formation in vitro, perhaps due to its intrinsic rigidity. To better understand yeast inner kinetochore assembly, we developed a one-step protocol to purify native inner kinetochore subcomplexes for structural studies. We performed cryo-electron microscopy on the purifications and generated density maps of four separate inner kinetochore complexes, two of which had not previously been visualized and may represent intermediate assembly states. We identified an Ndc10 trimerization domain that engages centromeric DNA and a pair of CBF3 complexes and is associated with substantial bending of centromeric DNA. Ndc10 trimerization is essential for kinetochore assembly and chromosome segregation. We propose that Ndc10 trimerization facilitates centromeric DNA bending to stabilize the centromeric nucleosome and inner kinetochore.

biochemistry↗

bioRxiv2025

Centromeres in the thermotolerant yeast K. marxianusmediate attachment to a single microtubule

Eukaryotic chromosome segregation requires spindle microtubules to attach to chromosomes through kinetochores. The chromosomal locus that mediates kinetochore assembly is the centromere and is epigenetically specified in most organisms by a centromeric histone H3 variant called CENP-A. An exception to this is budding yeast which have short, sequenced-defined point centromeres. In S. cerevisiae, a single CENP-A nucleosome is formed at the centromere and is sufficient for kinetochore assembly. The thermophilic budding yeast Kluyveromyces marxianus also has a point centromere but its length is nearly double the S. cerevisiae centromere and the number of centromeric nucleosomes and kinetochore attachment sites is unknown. Purification of native kinetochores from K. marxianus yielded a mixed population, with one subpopulation that appeared to consist of doublets, making it unclear whether K. marxianus shares the same attachment architecture as S. cerevisiae. Here, we demonstrate that though the doublet kinetochores have a functional impact on kinetochore strength, kinetochore localization throughout the cell cycle appears conserved between these two yeasts. In addition, whole spindle electron tomography demonstrates that a single microtubule binds to each chromosome. Single-molecule nucleosome mapping analysis suggests the presence of a single centromeric nucleosome. Taken together, we propose that the K. marxianus point centromere assembles a single centromeric nucleosome that mediates attachment to one microtubule.

cell biology↗

bioRxiv2024

Stable centromere association of the yeast histone variant Cse4 requires its essential N-terminal domain

Chromosome segregation relies on kinetochores that assemble on specialized centromeric chromatin containing a histone H3 variant. In budding yeast, a single centromeric nucleosome containing Cse4 assembles at a sequence-defined 125 bp centromere. Yeast centromeric sequences are poor templates for nucleosome formation in vitro, suggesting the existence of mechanisms that specifically stabilize Cse4 nucleosomes in vivo. The extended Cse4 N-terminal tail binds to the chaperone Scm3, and a short essential region called END within the N-terminal tail binds the inner kinetochore complex OA. To address the roles of these interactions, we utilized single molecule fluorescence assays to monitor Cse4 during kinetochore assembly. We found that OA and Scm3 independently stabilize Cse4 at centromeres via their END interaction. Scm3 binding to the Cse4 END is enhanced by Ipl1/Aurora B phosphorylation, identifying a previously unknown role for Ipl1 in ensuring Cse4 stability. Strikingly, an Ipl1 phosphomimetic mutation in the Cse4 END enhances Scm3 binding and can restore Cse4 recruitment in mutants defective in OA binding. Together, these data suggest that a key function of the essential Cse4 N-terminus is to ensure Cse4 localization at centromeres.

cell biology↗