Fission yeast ch-TOG/XMAP215 homologue Alp14 connects mitotic spindles with the kinetochore and is a component of the Mad2-dependent spindle checkpoint

The TOG/XMAP215-related proteins play a role in microtubule dynamics at its plus end. Fission yeast Alp14, a newly identified TOG/XMAP215 family prote in, is essential for proper chromosome segregation in concert with a second homologue Dis1. We show that the alp14 mutant fails to progress towards no rmal bipolar spindle formation. Intriguingly, Alp14 itself is a component o f the Mad2-dependent spindle checkpoint cascade, as upon addition of microt ubule-destabilizing drugs the alp14 mutant is incapable of maintaining high H1 kinase activity, which results in securin destruction and premature chr omosome separation. Live imaging of Alp14-green fluorescent protein shows t hat during mitosis, Alp14 is associated with the peripheral region of the k inetochores as well as with the spindle poles. This is supported by ChIP (c hromatin immunoprecipitation) and overlapping localization with the kinetoc hore marker Mis6. An intact spindle is required for Alp14 localization to t he kinetochore periphery, but not to the poles, These results indicate that the TOG/XMAP215 family may play a central role as a bridge between the kin etochores and the plus end of pole to chromosome microtubules.