The Dam1 ring binds to the E-hook of tubulin and diffuses along the microtubule.

There has been much effort in recent years aimed at understanding the molecular mechanism by which the Dam1 kinetochore complex is able to couple microtubule depolymerization to poleward movement. Both a biased diffusion and a forced walk model have been proposed, and several key functional aspects of Dam1-microtubule binding are disputed. Here, we investigate the elements involved in tubulin-Dam1 complex interactions and directly visualize Dam1 rings on microtubules in order to infer their dynamic behavior on the microtubule lattice and its likely relevance at the kinetochore. We find that the Dam1 complex has a preference for native tubulin over tubulin that is lacking its acidic C-terminal tail. Statistical mechanical analysis of images of Dam1 rings on microtubules, applied to both the distance between rings and the tilt angle of the rings with respect to the microtubule axis, supports a diffusive ring model. We also present a cryo-EM reconstruction of the Dam1 ring, likely the relevant assembly form of the complex for energy coupling during microtubule depolymerization in budding yeast. The present studies constitute a significant step forward by linking structural and biochemical observations toward a comprehensive understanding of the Dam1 complex

The James Webb Space Telescope Mission

Twenty-six years ago a small committee report, building on earlier studies, expounded a compelling and poetic vision for the future of astronomy, calling for an infrared-optimized space telescope with an aperture of at least $4m$. With the support of their governments in the US, Europe, and Canada, 20,000 people realized that vision as the $6.5m$ James Webb Space Telescope. A generation of astronomers will celebrate their accomplishments for the life of the mission, potentially as long as 20 years, and beyond. This report and the scientific discoveries that follow are extended thank-you notes to the 20,000 team members. The telescope is working perfectly, with much better image quality than expected. In this and accompanying papers, we give a brief history, describe the observatory, outline its objectives and current observing program, and discuss the inventions and people who made it possible. We cite detailed reports on the design and the measured performance on orbit.Comment: Accepted by PASP for the special issue on The James Webb Space Telescope Overview, 29 pages, 4 figure

Structure-function insights into the yeast Dam1 kinetochore complex

Faithful segregation of genetic material during cell division requires the dynamic but robust attachment of chromosomes to spindle microtubules during all stages of mitosis. This regulated attachment occurs at kinetochores, which are complex protein organelles that are essential for cell survival and genome integrity. In budding yeast, in which a single microtubule attaches per kinetochore, a heterodecamer known as the Dam1 complex (or DASH complex) is required for proper chromosome segregation. Recent years have seen a burst of structural and biophysical data concerning this interesting complex, which has caught the attention of the mitosis research field. In vitro, the Dam1 complex interacts directly with tubulin and self-assembles into ring structures around the microtubule surface. The ring is capable of tracking with depolymerizing ends, and a model has been proposed whereby the circular geometry of the oligomeric Dam1 complex allows it to couple the depolymerization of microtubules to processive chromosome movement in the absence of any additional energy source. Although it is attractive and simple, several important aspects of this model remain controversial. Additionally, the generality of the Dam1 mechanism has been questioned owing to the fact that there are no obvious Dam1 homologs beyond fungi. In this Commentary, we discuss recent structure-function studies of this intriguing complex

Subunit organization in the Dam1 kinetochore complex and its ring around microtubules

Chromosomes segregate by interaction of spindle microtubules with kinetochores. In budding yeast the Dam1 complex forms rings around microtubules and recapitulates the functionality of a kinetochore–microtubule attachment. Mapping of subunits within the complex and their organization within the ring has made it possible to generate a model of Dam1 ring assembly

The Dam1 ring binds to the E-hook of tubulin and diffuses along the microtubule.

There has been much effort in recent years aimed at understanding the molecular mechanism by which the Dam1 kinetochore complex is able to couple microtubule depolymerization to poleward movement. Both a biased diffusion and a forced walk model have been proposed, and several key functional aspects of Dam1-microtubule binding are disputed. Here, we investigate the elements involved in tubulin-Dam1 complex interactions and directly visualize Dam1 rings on microtubules in order to infer their dynamic behavior on the microtubule lattice and its likely relevance at the kinetochore. We find that the Dam1 complex has a preference for native tubulin over tubulin that is lacking its acidic C-terminal tail. Statistical mechanical analysis of images of Dam1 rings on microtubules, applied to both the distance between rings and the tilt angle of the rings with respect to the microtubule axis, supports a diffusive ring model. We also present a cryo-EM reconstruction of the Dam1 ring, likely the relevant assembly form of the complex for energy coupling during microtubule depolymerization in budding yeast. The present studies constitute a significant step forward by linking structural and biochemical observations toward a comprehensive understanding of the Dam1 complex

The Dam1 ring binds to the E-hook of tubulin and diffuses along the microtubule

There has been much effort in recent years aimed at understanding the molecular mechanism by which the Dam1 kinetochore complex is able to couple microtubule depolymerization to poleward movement. Both a biased diffusion and a forced walk model have been proposed, and several key functional aspects of Dam1-microtubule binding are disputed. Here, we investigate the elements involved in tubulin-Dam1 complex interactions and directly visualize Dam1 rings on microtubules in order to infer their dynamic behavior on the microtubule lattice and its likely relevance at the kinetochore. We find that the Dam1 complex has a preference for native tubulin over tubulin that is lacking its acidic C-terminal tail. Statistical mechanical analysis of images of Dam1 rings on microtubules, applied to both the distance between rings and the tilt angle of the rings with respect to the microtubule axis, supports a diffusive ring model. We also present a cryo-EM reconstruction of the Dam1 ring, likely the relevant assembly form of the complex for energy coupling during microtubule depolymerization in budding yeast. The present studies constitute a significant step forward by linking structural and biochemical observations toward a comprehensive understanding of the Dam1 complex

The Ndc80 kinetochore complex forms oligomeric arrays along microtubules

The Ndc80 complex is a key site of regulated kinetochore-microtubule attachment, but the molecular mechanism underlying its function remains unknown. Here we present a subnanometer resolution cryo-electron microscopy reconstruction of the human Ndc80 complex bound to microtubules, sufficient for precise docking of crystal structures of the component proteins. We find that Ndc80 binds the microtubule with a tubulin monomer repeat, recognizing α- and β-tubulin at both intra- and inter-dimer interfaces in a manner that is sensitive to tubulin conformation. Furthermore, Ndc80 complexes self-associate along protofilaments via interactions mediated by the amino-terminal tail of the Ndc80 protein, the site of phospho-regulation by the Aurora B kinase. Ndc80's mode of interaction with the microtubule and its oligomerization suggest a mechanism by which Aurora B could regulate the stability of load-bearing Ndc80-microtubule attachments