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 h omologs of the S. cerevisiae CDC27 and CDC16 proteins, which are tetra trico peptide repeat (TPR)-containing proteins essential for mitosis i n budding yeast. We find that the CDC27Hs and CDC16Hs proteins colocal ize to the centrosome at all stages of the mammalian cell circle, and to the mitotic spindle. Injection of affinity-purified anti-CDC27Hs an tibodies into logarithmically growing HeLa cells causes a highly repro ducible cell cycle arrest in metaphase with apparently normal spindle structure. We conclude that CDC27 and CDC16 are evolutionarily conserv ed components of the centrosome and mitotic spindle that control the o nset of postmetaphase events during mitosis.