Cell cycle control by Ca2+ in Saccharomyces cerevisiae.

We established an experimental system suitable for study of cell cycle regulation by Ca2+ in the yeast Saccharomyces cerevisiae. Systematic cell cycle analysis using media containing various concentrations of Ca2+, a Ca2(+)-ionophore (A23187), and a Ca2(+)-chelator [ethylenebis(oxyethylenenitrilo)]tetraacetic acid (EGTA) revealed that simultaneous addition of 10 microM A23187 and 10 mM EGTA to cells growing in a Ca2(+)-deficient medium at 22 degrees C caused rapid decrease in intracellular Ca content and resulted in transient G1 arrest followed by block mostly at G2/M, as revealed by flow cytometry. Recovery from G1 arrest was not due to coordinated initiation of DNA synthesis and bud emergence: unbudded cells with S or G2/M DNA were observed. Examination of terminal phenotype suggested that Ca2+ was required at all the stages of the cell cycle except for the initiation of DNA synthesis. The intracellular cAMP level decreased within 10 min of addition of A23187 and EGTA. No significant transient G1 arrest was observed in cells incubated with 8-Br-cAMP, or RAS2val19 and delta bcy1 mutants, which produce a high level of cAMP and have constitutively activated cAMP-dependent protein kinase, respectively. These results indicate that Ca2+ is essential for cell cycle progression and suggest that Ca2+ may regulate the cAMP level. This system will be useful for genetic and molecular studies on cell cycle events regulated by Ca2+.