Peng Yutian, Moritz Michelle, Han Xuemei, Giddings Thomas H, Lyon Andrew, Kollman Justin, Winey Mark, Yates John, Agard David A, Drubin David G, Barnes Georjana
Department of Molecular and Cell Biology, University of California, Berkeley, Berkeley, CA 94720.
Department of Biochemistry and Biophysics, Howard Hughes Medical Institute, University of California, San Francisco, San Francisco, CA 94158.
Mol Biol Cell. 2015 Jul 1;26(13):2505-18. doi: 10.1091/mbc.E14-12-1627. Epub 2015 May 13.
Casein kinase 1δ (CK1δ) family members associate with microtubule-organizing centers (MTOCs) from yeast to humans, but their mitotic roles and targets have yet to be identified. We show here that budding yeast CK1δ, Hrr25, is a γ-tubulin small complex (γTuSC) binding factor. Moreover, Hrr25's association with γTuSC depends on its kinase activity and its noncatalytic central domain. Loss of Hrr25 kinase activity resulted in assembly of unusually long cytoplasmic microtubules and defects in spindle positioning, consistent with roles in regulation of γTuSC-mediated microtubule nucleation and the Kar9 spindle-positioning pathway, respectively. Hrr25 directly phosphorylated γTuSC proteins in vivo and in vitro, and this phosphorylation promoted γTuSC integrity and activity. Because CK1δ and γTuSC are highly conserved and present at MTOCs in diverse eukaryotes, similar regulatory mechanisms are expected to apply generally in eukaryotes.
酪蛋白激酶1δ（CK1δ）家族成员在从酵母到人类的生物体内都与微管组织中心（MTOC）相关联，但其在有丝分裂中的作用和靶点尚未明确。我们在此表明，芽殖酵母的CK1δ，即Hrr25，是一种γ-微管蛋白小复合体（γTuSC）结合因子。此外，Hrr25与γTuSC的结合取决于其激酶活性及其非催化性中央结构域。Hrr25激酶活性的丧失导致异常长的细胞质微管组装以及纺锤体定位缺陷，分别与γTuSC介导的微管成核调控作用和Kar9纺锤体定位途径中的作用一致。Hrr25在体内和体外均可直接磷酸化γTuSC蛋白，且这种磷酸化促进了γTuSC的完整性和活性。由于CK1δ和γTuSC高度保守且存在于多种真核生物的MTOC中，预计类似的调控机制在真核生物中普遍适用。
