Nickel-Resistant Mutant of S. pombe 139 MOLECULAR BIOTECHNOLOGY Volume 32, 2006 RESEARCH 139 Molecular Biotechnology © 2006 Humana Press Inc. All rights of any nature whatsoever reserved. 1073–6085/2006/32:2/139–146/$30.00 *Author to whom all correspondence and reprint requests should be addressed. 1 Istanbul University, Faculty of Science, Department of Moleuclar Biology and Genetics, 34118 Vezneciler, Istanbul, Turkey. E-mail: atopal@Istanbul.edu.tr. 2 Instanbul University Research and Application Center for Biotechnology and Genetic Engineering 34118, Vezneciler, Istanbul, Turkey; 3 Istanbul University, Hasan Ali Yucel Education Faculty, Department of Primary Education, Division of Science Teacher Training, 34118 Vezneciler, Turkey. Abstract Nickel Resistance in Fission Yeast Associated With the Magnesium Transport System Aysegul Topal Sarikaya,* ,1,2 Gokhan Akman, 3 and Guler Temizkan, 1,2 We isolated and characterized a nickel (Ni 2+ )-resistant mutant (GA1) of Schizosaccharomyces pombe. This mutant strain displayed resistance to both Ni 2+ and Zn 2+ , but not to Cd 2+ , Co 2+ , and Cu 2+ . The growth rate of GA1 increased proportionally with increasing Mg 2+ concentrations until 50 mM Mg 2+ . The GA1 mutation phenotype suggests a defect in Mg 2+ uptake. Sequence analysis of the GA1 open reading frame (ORF) O13779, which is homologous to the prokaryotic and eukaryotic CorA Mg 2+ transport systems, revealed a point mutation at codon 153 (ccc to acc) resulting in a Pro153Thr substitution in the N-terminus of the CorA domain. Our results provide novel genetic information about Ni 2+ resistance in fission yeast. Specifically, that reducing Mg 2+ influx through the CorA Mg 2+ transport membrane protein confers Ni 2+ resistance in S. pombe. We also report that Ni 2+ ion detoxification of the fission yeast is related to histidine metabolism and pH. Index Entries: Schizosaccharomyces pombe; nickel resistance; Mg 2+ transport system; metal transport. 1. Introduction All organisms require heavy metal ions, such as the divalents Fe, Cu, Zn, Co, or Ni, at trace levels. However, crossing ion-specific threshold concentrations can render even minute amounts of these metals toxic to the cell. Nickel is an essential cofactor for a number of prokaryotic and eukaryotic enzymes, including urease, CO dehydrogenase, hydrogenase, and methyl coen- zyme M reductase (1). Nickel is a frequently encountered heavy metal in raw wastewater streams from various industries (2). It can become extremely toxic to eukaryotic and prokaryotic organisms at higher concentrations (3). At toxic levels, Ni 2+ inhibits synthesis of macromolecules such as RNA and protein (4). Nickel toxicity also alters the metabolism of carbohydrates and organic ions by interfering with the roles of other trace ele- ments, such as Mg 2+ and Fe 3+ (5). The Interna- tional Agency for Research on Cancer (IARC) states that some Ni 2+ compounds, including metal- lic Ni, may be carcinogenic to humans (www.eco- usa.net/toxics/nickel.shtml). All organisms have various detoxification mecha- nisms that protect them against heavy metal ions. Thus, intracellular heavy-metal-ion concentrations are tightly controlled (6). A series of homeostatic cellular mechanisms have evolved to maintain req- uisite intracellular metal ion concentrations and to jettison excess metal quantities (3). Nickel enters the cell mainly by the CorA sys- tem in bacteria (7). Eukaryotic homologs of the bacterial CorA Mg 2+ transporters have also been identified in the yeast Saccharomyces cerevisiae (8–10). Recently, Eitinger et al. (11) demonstrated that Nic1, a plasma membrane protein in S. pombe, plays a role in Ni 2+ transport.