title: Comparative study of the different mechanisms for zinc ion stress sensing in two cyanobacterial strains, Synechococcus sp. PCC 7942 and Synechocystis sp. PCC 6803.
abstract: In response to an increased level of Zn(2+), Synechococcus sp. PCC 7942 expresses SmtA, a metallothionein-like metal-chelating protein, while Synechocystis sp. PCC 6803 expresses ZiaA, a transporter of Zn(2+). 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(2+), we examined the cis-elements in the promoter regions of smtA and ziaA, as well as the binding affinities of recombinant SmtB and ZiaR proteins. The operator/promoter region of smtA included two palindromic sequences and that of ziaA included one. Electrophoretic mobility shift assay revealed that SmtB formed four different complexes with the operator/promoter region of smtA, whereas it formed only two different complexes with the corresponding region of ziaA. 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(2+) at higher concentrations than 16 μM. On the other hand, the corresponding Zn(2+) concentration is 128 μM. 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(2+) on the dissociation of these complexes are mainly associated with the structures of the repressors.
authors: Department of Bioresources, Faculty of Agriculture, Ehime University, 3-5-7 Tarumi, Matsuyama, Ehime 790-8566, Japan; Venture Business Laboratory, Ehime University, 3 Bunkyo-cho, Matsuyama, Ehime 790-8577, Japan.
authors: Eugene Hayato
authors: EH
authors: Morita
authors: Cell-Free Science and Technology Research Center, Ehime University, 2-5 Bunkyo-cho, Matsuyama, Ehime 790-8577, Japan.
authors: Satsuki
authors: S
authors: Kawamoto
authors: Department of Bioresources, Faculty of Agriculture, Ehime University, 3-5-7 Tarumi, Matsuyama, Ehime 790-8566, Japan.
authors: Shunnosuke
authors: S
authors: Abe
authors: Cell-Free Science and Technology Research Center, Ehime University, 2-5 Bunkyo-cho, Matsuyama, Ehime 790-8577, Japan; Present Address: Department of Biochemistry and Molecular Biology, Graduate School of Science and Engineering, Saitama University, 255 Shimo-Okubo, Sakura-ku, Saitama 338-8570, Japan.
authors: Yoshitaka
authors: Y
authors: Nishiyama
authors: Protein Research Institue, Osaka University, 3-2 Yamada-Oka, Suita, Osaka 565-0871, Japan.
authors: Takahisa
authors: T
authors: Ikegami
authors: Venture Business Laboratory, Ehime University, 3 Bunkyo-cho, Matsuyama, Ehime 790-8577, Japan; Cell-Free Science and Technology Research Center, Ehime University, 2-5 Bunkyo-cho, Matsuyama, Ehime 790-8577, Japan.
authors: Hidenori
authors: H
authors: Hayashi
keywords: Electrophoretic mobility shift assay (EMSA); operator/promoter; transcription factor; zinc ion binding