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Mol Biol Cell. 2015 Jul 1;26(13):2505-18. doi: 10.1091/mbc.E14-12-1627. Epub 2015 May 13.

Interaction of CK1δ with γTuSC ensures proper microtubule assembly and spindle positioning.

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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.
Department of Chemical Physiology, Scripps Research Institute, La Jolla, CA 92037.
Department of Molecular, Cellular, and Developmental Biology, University of Colorado, Boulder, Boulder, CO 80309.
Department of Molecular and Cell Biology, University of California, Berkeley, Berkeley, CA 94720


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.

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