THE ROLE OF SACCHAROMYCES-CEREVISIAE CDC40P IN DNA-REPLICATION AND MITOTIC SPINDLE FORMATION AND OR MAINTENANCE/

Successful progression. through the cell cycle requires the coupling o f mitotic spindle formation to DNA replication. In this report we pres ent evidence suggesting that, in Saccharomyces cerevisiae, the CDC40 g ene product is required to regulate both DNA replication and mitotic s pindle formation. The deduced amino acid sequence of CDC40 (455 amino acids) contains four copies of a beta-transducin-like repeat. Cdc40p i s essential only at elevated temperatures, as a complete deletion or a truncated protein (deletion of the C-terminal 217 amino acids in the cdc40-1 allele) results in normal vegetative growth at 23 degrees C, a nd cell cycle arrest at 36 degrees C. In the mitotic cell cycle Cdc40p is apparently required for at least two steps: (1) for entry into S p hase (neither DNA synthesis, nor mitotic spindle formation occurs at 3 6 degrees C and (2) for completion of S-phase (cdc40::LEU2 cells canno t complete the cell cycle when returned to the permissive temperature in the presence of hydroxyurea). The role of Cdc40p as a regulatory pr otein linking DNA synthesis, spindle assembly/maintenance, and maturat ion promoting factor (MPF) activity is discussed.