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  • 1
    Electronic Resource
    Electronic Resource
    ZntR is a Zn(II)-responsive MerR-like transcriptional regulator of zntA in Escherichia coli (1999)
    Oxford BSL : Blackwell Science Ltd
    Molecular microbiology 31 (1999), S. 0 
    Details
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: We have identified the promoter/operator region of the zntA gene of Escherichia coli and shown that Zn(II) is the primary inducer of expression of this Zn(II)/Cd(II) export gene. The promoter PzntA shows sequence similarities to the promoters of mercury resistance (mer ) operons, including a long spacer region containing an inverted repeat sequence. The gene encoding the transcriptional regulator of PzntA, designated zntR, has been identified from genome sequence data, by expression of the gene product and by insertional inactivation/complementation. The ZntR product is a member of the MerR family of transcriptional regulators and appears to act as a hypersensitive transcriptional switch. A hybrid MerR/ZntR protein has been constructed and indicates that the C-terminal region of ZntR recognizes Zn(II).
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-2958.1999.01229.x
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  • 2
    Electronic Resource
    Electronic Resource
    Deletion within the metallothionein locus of cadmium-tolerant Synechococcus PCC 6301 involving a highly iterated palindrome (HIP1) (1993)
    Oxford, UK : Blackwell Publishing Ltd
    Molecular microbiology 7 (1993), S. 0 
    Details
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: Genomic rearrangements involving amplification of metallothionein (MT) genes have been reported in metal-tolerant eukaryotes. Similarly, we have recently observed amplification and rearrangement of a prokaryotic MT locus, smt, in cells of Synechococcus PCC 6301 selected for Cd tolerance. Following the characterization of this locus, the altered smt region has now been isolated from a Cd-tolerant cell line, C3.2, and its nucleotide sequence determined. This has identified a deletion within smtB, which encodes a trans-acting repressor of smt transcription. Two identical palindromic octanucleotides (5′-GCGATC-GC-3′) traverse both borders of the excised element. This palindromic sequence is highly represented in the smt locus (7 occurrences in 1326 nucleotides) and analysis of the GenBank/EMBL /DDB J DNA Nucleotide Sequence Data Libraries reveals that this is a highly iterated palindrome (HIP1) in other known sequences from Synechococcus strains (estimated to occur at an average frequency of once every c. 664 bp). HIP1 is also abundant in the genomes of other cyanobacteria. The functional significance of smtB deletion and the possible role of HIP1 in genome plasticity and adaptation in cyanobacteria are discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-2958.1993.tb01110.x
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  • 3
    Electronic Resource
    Electronic Resource
    Isolation of a prokaryotic metallothionein locus and analysis of transcriptional control by trace metal ions (1993)
    Oxford, UK : Blackwell Publishing Ltd
    Molecular microbiology 7 (1993), S. 0 
    Details
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: In eukaryotes, metallothioneins (MTs) are involved in cellular responses to elevated concentrations of certain metal ions. We report the isolation and analysis of a prokaryotic MT locus from Synechococcus PCC 7942. The MT locus (smt) includes smtA, which encodes a class II MT, and a divergently transcribed gene, smtB. The sites of transcription initiation of both genes have been mapped and features within the smt operator-promoter region identified. Elevated concentrations of the ionic species of Cd, Co, Cr, Cu, Hg, Ni, Pb and Zn elicited an increase in the abundance of smtA transcripts. There was no detectable effect of elevated metal (Cd) on smtA transcript stability. Sequences upstream of smtA, fused to a promoterless lacZ gene, conferred metal-dependent β-galactosidase activity in Synechococcus PCC 7942 (strain R2-PIM8). At maximum permissive concentrations, Zn was the most potent elicitor in vivo, followed by Cu and Cd with slight induction by Co and Ni. The deduced SmtB polypeptide has similarity to the ArsR and CadC proteins involved in resistance to arsenate/arsenite/antimonite and to Cd, contains a predicted helix-turn-helix DNA-binding motif and is shown to be a repressor of transcription from the smtA operator-promoter.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-2958.1993.tb01109.x
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  • 4
    Electronic Resource
    Electronic Resource
    The role of cysteine residues in the transport of mercuric ions by the Tn501 MerT and MerP mercury-resistance proteins (1995)
    Osney Mead, Oxford OX2 0EL, UK : Blackwell Scientific Publications
    Molecular microbiology 17 (1995), S. 0 
    Details
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: Each cysteine residue in the MerT and MerP polypeptides of bacterial transposon Tn501 was replaced by serine, and the mercury-resistance phenotypes of the mutants were determined in Escherichia coli. Cys−24 and Cys−25 in the first transmembrane region of MerT were essential for transport of mercuric ions through the cytoplasmic membrane, and mutations Cys−76-Ser, Cys−82-Ser or Gly−38-Asp in MerT or Cys−36-Ser in MerP all reduced transport and resistance. Deletion of the merP gene slightly reduced mercuric ion resistance and transport, whereas a Cys−33-Ser mutation in MerP appears to block transport of mercuric ions by MerT. The effects of deleting merP on mutations in merT were tested. The 116-amino-acid MerT protein is sufficient for mercuric ion transport across the cytoplasmic membrane.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-2958.1995.mmi_17010025.x
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  • 5
    Electronic Resource
    Electronic Resource
    Guest Editorial (2003)
    Oxford, UK : Blackwell Publishing Ltd
    FEMS microbiology reviews 27 (2003), S. 0 
    Details
    ISSN: 1574-6976
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1016/S0168-6445(03)00040-8
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  • 6
    Electronic Resource
    Electronic Resource
    Zn(II) metabolism in prokaryotes (2003)
    Oxford, UK : Blackwell Publishing Ltd
    FEMS microbiology reviews 27 (2003), S. 0 
    Details
    ISSN: 1574-6976
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: It is difficult to over-state the importance of Zn(II) in biology. It is a ubiquitous essential metal ion and plays a role in catalysis, protein structure and perhaps as a signal molecule, in organisms from all three kingdoms. Of necessity, organisms have evolved to optimise the intracellular availability of Zn(II) despite the extracellular milieu. To this end, prokaryotes contain a range of Zn(II) import, Zn(II) export and/or binding proteins, some of which utilise either ATP or the chemiosmotic potential to drive the movement of Zn(II) across the cytosolic membrane, together with proteins that facilitate the diffusion of this ion across either the outer or inner membranes of prokaryotes. This review seeks to give an overview of the systems currently classified as altering Zn(II) availability in prokaryotes.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1016/S0168-6445(03)00041-X
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  • 7
    Electronic Resource
    Electronic Resource
    Regulation of glutamine synthetase genes in leaves of Phaseolus vulgaris (1991)
    Springer
    Plant molecular biology 17 (1991), S. 761-771 
    Details
    ISSN: 1573-5028
    Keywords: glutamine synthetase ; leaves ; light regulation ; nitrogen metabolism ; Phaseolus vulgaris ; photorespiration
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Glutamine synthetase (GS) activity increased over three-fold in developing primary leaves of Phaseolus vulgaris L. This increase was shown to be the result of differential expression of three members of the GS gene family: gln-α and gln-β, which encode cytosolic GS polypeptides, and gln-δ, which encodes the chloroplast-located GS. The gln-δ gene was the most highly expressed GS gene and was regulated in a complex manner with two different transcripts accumulating differentially during leaf development. This gene was expressed weakly in the dark and was induced strongly by lingt; this induction was shown not to be an indirect effect of photorespiration. In the long term, gln-δ showed increased expression in photorespiring compared with non-photorespiring leaves. However, in the short term, there was no induction of gln-δ following transfer of plants to photorespiratory conditions. These results suggest that regulation of gln-δ by photorespiration was the result of indirect, long-term effects on cellular metabolism. In general, in all these experiments, analysis of cytosolic versus chloroplastic GS polypeptides and of the GS isoenzyme profiles showed the same pattern of changes in abundance as that observed for the mRNAs suggesting that regulation of GS gene expression occurred primarily at the mRNA level. However, it was noteworthy that the δ isoenzyme remained at a high abundance in older leaves, grown in both light and dark, despite a decrease in abundance of gln-δ mRNA.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00037059
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  • 8
    Electronic Resource
    Electronic Resource
    Bacterial resistances to mercury and copper (1991)
    New York, N.Y. : Wiley-Blackwell
    Journal of Cellular Biochemistry 46 (1991), S. 106-114 
    Details
    ISSN: 0730-2312
    Keywords: copper ; heavy metal ; ion transport ; mercury ; resistance ; Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Chemistry and Pharmacology , Medicine
    Notes: Heavy metals are toxic to living organisms. Some have no known beneficial biological function, while others have essential roles in physiological reactions. Mechanisms which deal with heavy metal stress must protect against the deleterious effects of heavy metals, yet avoid depleting the cell of a heavy metal which is also an essential nutrient. We describe the mechanims of resistance in Escherichia coli to two different heavy metals, mercury and copper. Resistance of E. coli to mercury is reasonably well understood and is known to occur by transport of mercuric ions into the cytoplasmic compartment of the bacterial cell and subsequent reductive detoxification of mercuric ions. Recent mutational analysis has started to uncover the mechanistic detail of the mercuric ion transport processes, and has shown the essential nature of cysteine residues in transport of Hg(II). Resistance to copper is much less well understood, but is known to involve the increased export of copper from the bacterial cell and modification of the copper; the details of the process are still being elucidated.Expression of both metal resistance determinants is regulated by the corresponding cation. In each case the response enables the maintenance of cellular homeostasis for the metal. The conclusions drawn allow us to make testable predictions about the regulation of expression of resistance to other heavy metals.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jcb.240460204
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