Premium
The ZnuABC high‐affinity zinc uptake system and its regulator Zur in Escherichia coli
Author(s) -
Patzer Silke I.,
Hantke Klaus
Publication year - 1998
Publication title -
molecular microbiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.857
H-Index - 247
eISSN - 1365-2958
pISSN - 0950-382X
DOI - 10.1046/j.1365-2958.1998.00883.x
Subject(s) - operon , biology , mutant , escherichia coli , complementation , lac operon , microbiology and biotechnology , biochemistry , repressor , fusion protein , gene , ferrichrome , regulator gene , regulation of gene expression , gene expression , recombinant dna , bacterial outer membrane
In Escherichia coli , lacZ operon fusions were isolated that were derepressed under iron repletion and repressed under iron depletion. Two fusions were localized in genes that formed an operon whose gene products had characteristics of a binding protein‐dependent transport system. The growth defect of these mutants on TY medium containing 5 mM EGTA was compensated for by the addition of Zn 2+ . In the presence of 0.5 mM EGTA, only the parental strain was able to take up 65 Zn 2+ . This high‐affinity transport was energized by ATP. The genes were named znuACB (for zinc uptake; former name yebLMI ) and localized at 42 min on the genetic map of E. coli . At high Zn 2+ concentrations, the znu mutants took up more 65 Zn 2+ than the parental strain. The high‐affinity 65 Zn 2+ uptake was repressed by growth in the presence of 10 μM Zn 2+ . A znuA–lacZ operon fusion was repressed by 5 μM Zn 2+ and showed a more than 20‐fold increase in β‐galactosidase activity when Zn 2+ was bound to 1.5 μM TPEN [tetrakis‐(2‐pyridylmethyl) ethylenediamine]. To identify the Zn 2+ ‐dependent regulator, constitutive mutants were isolated and tested for complementation by a gene bank of E. coli . A complementing gene, yjbK of the E. coli genome, was identified and named zur (for zinc uptake regulation). The Zur protein showed 27% sequence identity with the iron regulator Fur. High‐affinity 65 Zn 2+ transport of the constitutive zur mutant was 10‐fold higher than that of the uninduced parental strain. An in vivo titration assay suggested that Zur binds to the bidirectional promoter region of znuA and znuCB .