An SmtB-like repressor from <i>Synechocystis</i> PCC 6803 regulates a zinc exporter

Proceedings of the National Academy of Sciences of the United States of America - Tập 95 Số 18 - Trang 10728-10733 - 1998
Craig Thelwell1, Nigel J. Robinson1, Jim Cavet1
1Department of Biochemistry and Genetics, The Medical School, University of Newcastle, NE2 4HH, United Kingdom

Tóm tắt

ORF slr0798, now designated ziaA , from Synechocystis PCC 6803 encodes a polypeptide with sequence features of heavy metal transporting P-type ATPases. Increased Zn 2+ tolerance and reduced 65 Zn accumulation was observed in Synechococcus PCC 7942, strain R2-PIM8( smt ), containing ziaA and upstream regulatory sequences, compared with control cells. Conversely, reduced Zn 2+ tolerance was observed following disruption of ziaA in Synechocystis PCC 6803, and ziaA -mediated restoration of Zn 2+ tolerance has subsequently been used as a selectable marker for transformation. Nucleotide sequences upstream of ziaA , fused to a promoterless lacZ gene, conferred Zn 2+ -dependent β-galactosidase activity when introduced into R2-PIM8( smt ). The product of ORF sll0792, designated ZiaR, is a Zn 2+ -responsive repressor of ziaA transcription. Reporter gene constructs lacking ziaR conferred elevated Zn 2+ -independent expression from the ziaA operator–promoter in R2-PIM8( smt ). Gel retardation assays detected ZiaR-dependent complexes forming with the zia operator–promoter and ZiaR–DNA binding was enhanced by treatment with a metal-chelator in vitro . Two mutants of ZiaR (C71S/C73S and H116R) bound to, and repressed expression from, the ziaA operator–promoter but were unable to sense Zn 2+ . Metal coordination to His-imidazole and Cys-thiolate ligands at these residues of ZiaR is thus implicated in Zn 2+ -perception by Synechocystis PCC 6803.

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Proceedings of the National Academy of Sciences of the United States of America

Tập 95 Số 18

10728-10733

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