The Nup107-160 complex and γ-TuRC regulate microtubule polymerization at kinetochores

The metazoan nuclear pore complex (NPC) disassembles during mitosis, and many of its constituents distribute onto spindles and kinetochores, including the Nup107-160 sub-complex. We have found that Nup107-160 interacts with the γ-tubulin ring complex (γ-TuRC), an essential and conserved microtubule nucleator, and recruits γ-TuRC to unattached kinetochores. The unattached kinetochores nucleate microtubules in a manner that is regulated by Ran GTPase; such microtubules contribute to the formation of kinetochore fibres (k-fibres), microtubule bundles connecting kinetochores to spindle poles. Our data indicate that Nup107-160 and γ-TuRC act cooperatively to promote spindle assembly through microtubule nucleation at kinetochores: HeLa cells lacking Nup107-160 or γ-TuRC were profoundly deficient in kinetochore-associated microtubule nucleation. Moreover, co-precipitated Nup107-160-γ-TuRC complexes nucleated microtubule formation in assays using purified tubulin. Although Ran did not regulate microtubule nucleation by γ-TuRC alone, Nup107-160-γ-TuRC complexes required Ran-GTP for microtubule nucleation. Collectively, our observations show that Nup107-160 promotes spindle assembly through Ran-GTP-regulated nucleation of microtubules by γ-TuRC at kinetochores, and reveal a relationship between nucleoporins and the microtubule cytoskeleton.