The budding yeast proteins Spc24p and Spc25p interact with Ndc80p and Nuf2p at the kinetochore and are important for kinetochore clustering and checkpoint control

Here, we show that the budding yeast proteins Ndc80p, Nuf2p, Spc24p and Spc 25p interact at the kinetochore, Consistently, Ndc80p, Nuf2p, Spc24p and Sp c25p associate with centromere DNA in chromatin immunoprecipitation experim ents, and SPC24 interacts genetically with MCM21 encoding a kinetochore com ponent. Moreover, although conditional lethal spc24-2 and spc25-7 cells for m a mitotic spindle, the kinetochores remain in the mother cell body and fa il to segregate the chromosomes. Despite this defect in chromosome segregat ion, spc24-2 and spc25-7 cells do not arrest in metaphase in response to ch eckpoint control. Furthermore, spc24-2 cells showed a mitotic checkpoint de fect when microtubules were depolymerized with nocodazole, indicating that Spc24p has a function in checkpoint control. Since Ndc80p, Nuf2p and Spc24p are conserved proteins, it is likely that similar complexes are part of th e kinetochore in other organisms.