Abstract
Kinetochores are the chromosomal attachment points for spindle microtubules. They are also signaling hubs that control major cell cycle transitions and coordinate chromosome folding. Most well-studied eukaryotes rely on a conserved set of factors, which are divided among two loosely-defined groups, for these functions. Outer kinetochore proteins contact microtubules or regulate this contact directly. Inner kinetochore proteins designate the kinetochore assembly site by recognizing a specialized nucleosome containing the H3 variant Cse4/CENP-A. We previously determined the structure, resolved by cryo-electron microscopy (cryo-EM), of the yeast Ctf19 complex (Ctf19c, homologous to the vertebrate CCAN), providing a high-resolution view of inner kinetochore architecture (Hinshaw and Harrison, 2019). We now extend these observations by reporting a near-atomic model of the Ctf3 complex, the outermost Ctf19c sub-assembly seen in our original cryo-EM density. The model is sufficiently well-determined by the new data to enable molecular interpretation of Ctf3 recruitment and function.
Highlights
Inner kinetochore proteins, members of the Ctf19c, constitute the foundation of the kinetochore; they both recognize Cse4/CENP-A and recruit microtubule-interacting outer kinetochore proteins (Musacchio and Desai, 2017)
Both Scc2/4 recruitment and stable microtubule binding at later stages of the cell cycle depend on the conserved Ctf3/CENP-I complex (Ctf3c) (Hara et al, 2018; Lang et al, 2018; Natsume et al, 2013)
We present a cryo-electron microscopy (cryo-EM) structure of the yeast Ctf3c, which resolves the overall organization of the complex, shows how Ctf3 binds Mcm16/ 22, and clarifies Ctf3c recruitment to the larger Ctf19c
Summary
Members of the Ctf19c, constitute the foundation of the kinetochore; they both recognize Cse4/CENP-A and recruit microtubule-interacting outer kinetochore proteins (Musacchio and Desai, 2017) Many of these factors were originally cloned and characterized for their contributions to faithful mitotic chromosome segregation (Hinshaw and Harrison, 2018). Recent findings suggest a handoff between Ctf19c-dependent microtubule contact points, whereby the link between centromeric DNA and spindle microtubules shifts between chromosomal tethers during the course of the cell cycle (Bock et al, 2012; Hara et al, 2018) Understanding coordination of these diverse activities requires a structural picture of the inner kinetochore.
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