Comparative study of the different mechanisms for zinc ion stress sensing in two cyanobacterial strains, <i>Synechococcus</i> sp. PCC 7942 and <i>Synechocystis</i> sp. PCC 6803

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    • Morita Eugene Hayato
    • Department of Bioresources, Faculty of Agriculture, Ehime University|Venture Business Laboratory, Ehime University
    • Abe Shunnosuke
    • Department of Bioresources, Faculty of Agriculture, Ehime University
    • Nishiyama Yoshitaka
    • Cell-Free Science and Technology Research Center, Ehime University|Department of Biochemistry and Molecular Biology, Graduate School of Science and Engineering, Saitama University
    • Hayashi Hidenori
    • Venture Business Laboratory, Ehime University|Cell-Free Science and Technology Research Center, Ehime University


In response to an increased level of Zn<sup>2+</sup>, <i>Synechococcus</i> sp. PCC 7942 expresses SmtA, a metallothionein-like metal-chelating protein, while <i>Synechocystis</i> sp. PCC 6803 expresses ZiaA, a transporter of Zn<sup>2+</sup>. The gene expression of these proteins is regulated by repressor protein, SmtB and ZiaR, respectively. In spite of contributing to different response systems, both repressor proteins belong to the ArsR family and are highly homologous to each other. To understand the different systems responsible for dealing with excess Zn<sup>2+</sup>, we examined the <i>cis</i>-elements in the promoter regions of <i>smtA</i> and <i>ziaA</i>, as well as the binding affinities of recombinant SmtB and ZiaR proteins. The operator/promoter region of <i>smtA</i> included two palindromic sequences and that of <i>ziaA</i> included one. Electrophoretic mobility shift assay revealed that SmtB formed four different complexes with the operator/promoter region of <i>smtA</i>, whereas it formed only two different complexes with the corresponding region of <i>ziaA</i>. For ZiaR, the corresponding results were quite the same as those for SmtB. Furthermore, the complex formation between SmtB and operator/promoter regions is inhibited in the presence of Zn<sup>2+</sup> at higher concentrations than 16 <symbol>m</symbol>M. On the other hand, the corresponding Zn<sup>2+ </sup>concentration is 128 <symbol>m</symbol>M. These results demonstrate that the degrees of protein-DNA complex formation between repressor proteins and the operator/promoter regions of regulated genes depend on the structures of the operator/promoter regions, and the effects of Zn<sup>2+ </sup>on the dissociation of these complexes are mainly associated with the structures of the repressors.<br>



    BIOPHYSICS 8(0), 103-109, 2012

    The Biophysical Society of Japan


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