ASURA (PHB2) knockdown has been known to cause premature loss of sister chromatid cohesion, and disrupt the localization of several outer plate proteins to the kinetochore. As a result, cells are arrested at mitotic phase and chromosomes fail to congress to the metaphase plate. In this study, we further clarified the mechanism underlying ASURA function on chromosome congression. Interestingly, ASURA is not specifically localized at the kinetochore during mitotic phase, unlike other kinetochore proteins which construct the kinetochore. Electron microscopy (EM) observation showed that ASURA is required for proper kinetochore formation. By the partial depletion of ASURA, kinetochore maturation is impaired, and kinetochores showing fibrillar balls without a well-defined outer plates are often observed. Moreover, even when the outer plates of kinetochores are constructed, most showed structures stretched and/or distended from the centromere, which resembled premature kinetochores at prometaphase, indicating that the constructed kinetochore plates are less rigid against tension derived from kinetochore microtubule pulling forces. We concluded that ASURA is an essential protein for complete kinetochore development, although ASURA is not being integrated to the kinetochore. These results highlight the uniqueness of ASURA as a kinetochore protein.
A plant-and prokaryote-conserved domain (PPC) has previously been found in AT-hook motif nuclear localized protein 1 (AHL1) localized in the nuclear matrix of Arabidopsis thaliana (AtAHL1). AtAHL1 has a DNA-binding function. Mutation analyses of AtAHL1 has previously revealed that the hydrophobic region of the PPC domain is essential for its nuclear localization. In this study, the PPC of the hyperthermophilic archaebacterium Pyrococcus horikoshii (PhPPC) was crystallized using the hanging-drop vapour-diffusion method. The crystals belonged to the hexagonal space group P6 3 22, with unitcell parameters a = b = 53.69, c = 159.2 Å . Data were obtained at 100 K, with diffraction being observed to a resolution of 1.7 Å . A complete data set from crystals of the SeMet-substituted protein was also obtained.
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