CDC27HS COLOCALIZES WITH CDC16HS TO THE CENTROSOME AND MITOTIC SPINDLE AND IS ESSENTIAL FOR THE METAPHASE TO ANAPHASE TRANSITION

have isolated cDNAs and raised antibodies corresponding to the human homologs of the S. cerevisiae CDC27 and CDC16 proteins, which are tetratrico peptide repeat (TPR)-containing proteins essential for mitosis in budding yeast. We find that the CDC27Hs and CDC16Hs proteins colocalize to the centrosome at all stages of the mammalian cell circle, and to the mitotic spindle. Injection of affinity-purified anti-CDC27Hs antibodies into logarithmically growing HeLa cells causes a highly reproducible cell cycle arrest in metaphase with apparently normal spindle structure. We conclude that CDC27 and CDC16 are evolutionarily conserved components of the centrosome and mitotic spindle that control the onset of postmetaphase events during mitosis.