A YEAST HEAT-SHOCK TRANSCRIPTION FACTOR (HSF1) MUTANT IS DEFECTIVE INBOTH HSC82 HSP82 SYNTHESIS AND SPINDLE POLE BODY DUPLICATION/

Cdc28 is a cyclin-dependent protein kinase of Saccharomyces cerevisiae that is required for the G(1)/S and G(2)/M transitions of the cell di vision cycle, All previously described cdc28 mutants aside from cdc28- lN arrest division specifically in the G(1) phase, cdc28-lN arrests di vision in G(2)/mitosis, We show here that the cdc28-109 mutant exhibit s a mixed cell division arrest at 37 degrees C with cells in both the G(1) and G(2) phases, In order to identify proteins that functionally interact with Cdc28, we isolated mutants that are colethal with cdc28- 109 at its permissive temperature, We describe here our phenotypic ana lysis of two such mutants, hsf1-82 and ydj1-10, that affect the heat s hock transcription factor and a yeast dnaj-like protein chaperone, res pectively, hsf1-82 and ydj1-10 temperature-sensitive mutants arrest th e cell division cycle at several stages. However, one predominant clas s of cells in both mutants was arrested with a large bud and a single vertex of microtubules, Electron microscopic analysis of such hsf1-82 cells showed that they contained an unduplicated spindle pole body wit h an enlarged half-bridge. Two-dimensional gel electrophoresis of tota l cell proteins revealed that the hsf1-82 cells were specifically defe ctive in the expression of the Hsc82 and HspS2 proteins, Furthermore, the hsf1-82 mutation was suppressed by the HSC82 gene on a multicopy p lasmid that restored Hsc82 protein to high levels in these cells, Thes e results show that Hsf1 is required for spindle pole body duplication at 37 degrees C.