Metal ion requirements for the proliferation of Saccharomyces cerevisiae were investigated. We used bis-(o-aminophenoxy)-ethane-N,N,N',N'-tetraacetic acid (BAPTA), a relatively acid tolerant chelator, to reduce the free metal ion concentrations in culture media. Chelatable metal ions were added back individually and in combination. In addition to a requirement for approximately 10 pM external free Zn2+ we found an interchangeable requirement for either 66 nM free Ca2+ or only 130 pM free Mn2+. Cells depleted of Mn2+ and Ca2+ arrested as viable cells with 2 N nuclei and tended to have very small minibuds. In the absence of added Mn2+, robust growth required approximately 60 microM total internal Ca2+. In the presence of added Mn2+, robust growth continued even when internal Ca2+ was < 3% this level. Chelator-free experiments showed that MnCl2 strongly and CaCl2 weakly restored high-temperature growth of cdc1ts strains which similarly arrest as viable cells with 2 N nuclear contents and small buds. Its much greater effectiveness compared with Ca2+ suggests that Mn2+ is likely to be a physiologic mediator of bud and nuclear development in yeast. This stands in marked contrast to a claim that Ca2+ is uniquely required for cell-cycle progression in yeast. We discuss the possibility that Mn2+ may function as an intracellular signal transducer and how this possibility relates to previous claims of Ca2+'s roles in yeast metabolism.

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