An SmtB-like repressor from Synechocystis PCC 6803 regulates a zinc exporter.
ORF slr0798, now designated ziaA, from Synechocystis PCC 6803 encodes a polypeptide with sequence features of heavy metal transporting P-type ATPases. Increased Zn2+ tolerance and reduced 65Zn accumulation was observed in Synechococcus PCC 7942, strain R2-PIM8(smt), containing ziaA and upstream regulatory sequences, compared with control cells. Conversely, reduced Zn2+ tolerance was observed following disruption of ziaA in Synechocystis PCC 6803, and ziaA-mediated restoration of Zn2+ tolerance has subsequently been used as a selectable marker for transformation. Nucleotide sequences upstream of ziaA, fused to a promoterless lacZ gene, conferred Zn2+-dependent beta-galactosidase activity when introduced into R2-PIM8(smt). The product of ORF sll0792, designated ZiaR, is a Zn2+-responsive repressor of ziaA transcription. Reporter gene constructs lacking ziaR conferred elevated Zn2+-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 Zn2+. Metal coordination to His-imidazole and Cys-thiolate ligands at these residues of ZiaR is thus implicated in Zn2+-perception by Synechocystis PCC 6803.
Thelwell
C
C
Department of Biochemistry and Genetics, The Medical School, University of Newcastle, NE2 4HH, United Kingdom.
Robinson
N J
NJ
Turner-Cavet
J S
JS
D001426:Bacterial Proteins / Q000502:physiology*; D001483:Base Sequence; D002352:Carrier Proteins / Q000235:genetics* / Q000378:metabolism; D002451:Cell Compartmentation; D002614:Chelating Agents; D000458:Cyanobacteria / Q000235:genetics*; D017931:DNA Primers; D004268:DNA-Binding Proteins / Q000502:physiology*; D015964:Gene Expression Regulation, Bacterial / Q000502:physiology*; D017136:Ion Transport; D009875:Operator Regions, Genetic; D011401:Promoter Regions, Genetic; D011994:Recombinant Proteins / Q000235:genetics / Q000378:metabolism; D012097:Repressor Proteins / Q000502:physiology*; D014158:Transcription, Genetic; D015032:Zinc / Q000378:metabolism*
D001426:Bacterial Proteins; D002352:Carrier Proteins; D002614:Chelating Agents; D017931:DNA Primers; D004268:DNA-Binding Proteins; D011994:Recombinant Proteins; D012097:Repressor Proteins; D015032:Zinc