The γ-tubulin ring complex (γ-TuRC) is a key part of microtubule-organizing centers (MTOCs) that control microtubule polarity, organization and dynamics in eukaryotes. Understanding regulatory mechanisms of γ-TuRC function is of fundamental importance, as this complex is central to many cellular processes, including chromosome segregation, fertility, neural development, T-cell cytotoxicity and respiration. The fission yeast microtubule motor kinesin-14 Pkl1 regulates mitosis by binding to the γ-tubulin small complex (γ-TuSC), a subunit of γ-TuRC. Here we investigate the binding mechanism of Pkl1 to γ-TuSC and its functional consequences using genetics, biochemistry, peptide assays and cell biology approaches in vivo and in vitro. We identify two critical elements in the Tail domain of Pkl1 that mediate γ-TuSC binding and trigger release of γ-tubulin from γ-TuRC. Such action disrupts the MTOC and results in failed mitotic spindle assembly. This study is the first demonstration that a motor protein directly affects the structural composition of the γ-TuRC, and we provide details of this mechanism that may be of broad biological importance.
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