The tetrameric kinesin Kif25 suppresses pre-mitotic centrosome separation to establish proper spindle orientation.

Microtubules tether centrosomes together during interphase. How this is accomplished and what benefit it provides to the cell is not known. We have identified a bipolar, minus-end-directed kinesin, Kif25, that suppresses centrosome separation. Kif25 is required to prevent premature centrosome separation during interphase. We show that premature centrosome separation leads to microtubule-dependent nuclear translocation, culminating in eccentric nuclear positioning that disrupts the cortical spindle positioning machinery. The activity of Kif25 during interphase is required to maintain a centred nucleus to ensure the spindle is stably oriented at the onset of mitosis.