Staurosporine is an antibiotic that specifically inhibits protein kinase C. Fourteen staurosporine- and temperature-sensitive (stt) mutants of Saccharomyces cerevisiae were isolated and characterized. These mutants were divided into ten complementation groups, and characterized for their cross-sensitivity to K-252a, neomycin, or CaCl2. The STT1 gene was cloned and sequenced. The nucleotide sequence of the STT1 gene revealed that STT1 is the same gene as PKC1. The STT1 gene conferred resistance to staurosporine on wild-type cells, when present on a high copy number plasmid. STT1/stt1::HIS3 diploid cells were more sensitive to staurosporine than STT1/STT1 diploid cells. Analysis of temperature-sensitive stt1 mutants showed that the STT1 gene product functioned in S or G2/M phase. These results suggest that a protein kinase (the STT1 gene product) is one of the essential targets of staurosporine in yeast cells.

The grpE gene is a heat shock gene of Escherichia coh whose product functions as a chaperone to (re)fold proteins. We found a yeast homologue of grpE and designated it YGEl. YGEI can replace grpE in E. coli, indicating that YGEl is a functional homologue of grpE. Deletion of YGEI is lethal. During depletion of the Ygel product, mitochondria are sequestered in mother cells thereby accumulating cells without mitochondria, suggesting that Ygel protein plays a pivotal role m maintaining mitochondrial functions.

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