The Family of SMF Metal Ion Transporters in Yeast Cells*
- From the Department of Biochemistry, The George S. Wise Faculty of Life Sciences, Tel Aviv University, Tel Aviv 69978, Israel
Abstract
Metal ions are vital for all organisms, and metal ion transporters play a crucial role in maintaining their homeostasis. The yeast (Saccharomyces cerevisiae) Smf transporters and their homologs in other organisms have a central role in the accumulation of metal ions and their distribution in different tissues and cellular organelles. In this work we generated null mutations in each individual SMF gene in yeast as well as in all combinations of the genes. Each null mutation exhibited sensitivity to metal ion chelators at different concentrations. The combination of null mutants ΔSMF1 + ΔSMF2and the triple null mutant Δ3SMF failed to grow on medium buffered at pH 8 and 7.5, respectively. Addition of 5 μmcopper or 25 μm manganese alleviated the growth arrest at the high pH or in the presence of the chelating agent. The transport of manganese was analyzed in the triple null mutant and in this mutant expressing each Smf protein. Although overexpression of Smf1p and Smf2p resulted in uptake that was higher than wild type cells, the expression of Smf3p gave no significant uptake above that of the triple mutant Δ3SMF. Western analysis with antibody against Smf3p indicated that this transporter does not reach the plasma membrane and may function at the Golgi or post-Golgi complexes. The iron uptake resulting from expression of Smf1p and Smf2p was analyzed in a mutant in which its iron transporters FET3and FET4 were inactivated. Overexpression of Smf1p gave rise to a significant iron uptake that was sensitive to the sodium concentrations in the medium. We conclude that the Smf proteins play a major role in copper and manganese homeostasis and, under certain circumstances, Smf1p may function in iron transport into the cells.
Footnotes
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↵* This project was funded by the BMBF and supported by BMBF's International Bureau at the DLR.The costs of publication of this article were defrayed in part by the payment of page charges. The article must therefore be hereby marked “advertisement” in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.
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↵‡ To whom correspondence should be addressed: Tel.: 972-3-640-6017; Fax: 972-3-640-6018; E-mail: nelson@post.tau.ac.il.
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Published, JBC Papers in Press, August 4, 2000, DOI 10.1074/jbc.M004611200
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↵2 A. Cohen, H. Nelson, and N. Nelson, unpublished results.
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↵3 A. Sacher, A. Cohen, and N. Nelson, manuscript in preparation.
- Abbreviations:
- MES
-
4-morpholineethanesulfonic acid
- kb
-
kilobase(s)
- PCR
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polymerase chain reaction
- MOPS
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4-morpholinepropanesulfonic acid
- TM
-
transmembrane domain
- t-SNARE
-
target SNAP receptor
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- Received May 28, 2000.
- Revision received July 26, 2000.
- The American Society for Biochemistry and Molecular Biology, Inc.
