The regulation of cell division in yeast by magnesium

Cells of the fission yeast, Schizosaccharomyces pombe, and the budding yeast, Kluyveromyces fragilis, fail to divide in Mg-free minimal media but can be induced to divide synchronously on restoration of Mg to “exhausted” cultures. Mg-depleted S. pombe, cells appear abnormally long, lack cell plates and possess elongated nuclei. This, together with evidence of a late cell cycle arrest by the ionophore A23187, suggests that specific Mg limitation blocks cells late in the G2 phase of the cell cycle. Moreover, analysis of cell Mg in cultures synchronized by various techniques reveals that there is a fairly steady fall in Mg concentration as cells grow, terminating in a rapid influx of Mg just before division. These results lead to the hypothesis that intracellular Mg concentration is the transducer for size and consequently time, related control of the cell cycle.