Characterization of the transcriptional response to Mg ²⁺ starvation in Saccharomyces cerevisiae.
Gerlinde Wiesenberger, Jochen Stadler, Rudolf Schweyen
MFPL, Department of Genetics, University of Vienna, Dr. Bohrgasse 9, Vienna, 1030, Austria

Whole genome microarray experiments were performed to learn about the cellular processes involved in Mg ²⁺ transport and the mechanisms allowing cells to cope with low Mg ²⁺ availability. The expression profile of cells grown in 1 mM Mg ²⁺ was compared to that of cells shifted to Mg ²⁺ free medium. A striking portion of genes upregulated upon Mg ²⁺ depletion is also induced by elevated Ca ²⁺ > and/or alkalization (Yoshimoto et al., (2002) J. Biol. Chem. 277, 31079-31088; Viladevall et al., (2004) J. Biol. Chem. 279, 43614-43624). Among the genes significantly upregulated by Mg ²⁺ starvation, Ca ²⁺ stress and alkalisation are ENA1 (encoding a P-type ATPase Na ⁺ pump) and PHO89 (encoding a Na ⁺ /P _i co-transporter). By Northern blot experiments we were able to show (i) that both genes are indeed specifically induced by Mg ²⁺ depletion and (ii) that upregulation of both genes is dependent on the Calcineurin/Crz1p signalling pathway. Upon Mg ²⁺ starvation GFP-tagged Crz1p (transcription factor mediating Ca-signalling) is translocated into the nucleus. Currently, we are investigating whether Mg ²⁺ starvation causes a cytoplasmic Ca ²⁺ pulse similar to Ca ²⁺ stress, alkalisation and other conditions such as hyper- and hypo-osmotic stress. Furthermore, we are attempting to find the possible source of the Ca ²⁺ signal.

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