PMID:11243806
| Citation |
Leonhartsberger, S, Huber, A, Lottspeich, F and Böck, A (2001) The hydH/G Genes from Escherichia coli code for a zinc and lead responsive two-component regulatory system. J. Mol. Biol. 307:93-105 |
|---|---|
| Abstract |
The hydH/G genes from Escherichia coli code for a two-component regulatory system that has been implicated in the regulation of hydrogenase 3 formation. In a detailed study of the function of HydH/G employing hycA'-'lacZ reporter gene fusions, it was shown that HydH/G indeed led to a stimulation of activation of the hycA promoter responsible for hydrogenase 3 synthesis but only when hydG is overexpressed from a plasmid in a strain lacking FhlA. Since the stimulation was not observed with an fdhF'-'lacZ fusion, and since it was independent from a functional hydH gene product, it must be considered as unspecific cross-talk. An extensive search for the actual physiological signal of HydH/G showed that the system responds to high concentrations of zinc or lead in the medium. Expression of zraP, a gene inversely oriented to hydH/G whose product seems to be involved in acquisition of tolerance to high Zn(2+) concentrations, is stimulated by high Zn(2+) and Pb(2+) concentrations and this stimulation requires both HydH and HydG. Purified HydG in the presence of phosphoryl donors binds to a region within the zraP-hydHG intergenic region that is characterised by two inverted repeats separated by a 14 bp spacer. Putative -12/-24 sigma(54)-dependent promoter motifs are present upstream of both the zraP and the hydHG transcriptional units; in accordance, transcription of zraP is strictly dependent on the presence of a functional rpoN gene. The expression of hydH/G is autoregulated: high Zn(2+) and Pb(2+) concentrations lead to a significant increase of the HydG protein content which took place only in a hydH(+) genetic background. Since HydH binds to membranes tightly, it is assumed that the HydH/G system senses high periplasmic Zn(2+) and Pb(2+) concentrations and contributes to metal tolerance by activating the expression of zraP. The redesignation of hydH/G as zraS/R is suggested. |
| Links |
PubMed Online version:10.1006/jmbi.2000.4451 |
| Keywords |
Bacterial Proteins/genetics; Bacterial Proteins/metabolism; Bacterial Proteins/physiology; Base Sequence; Cloning, Molecular; DNA Footprinting; DNA, Bacterial/analysis; DNA, Bacterial/metabolism; DNA-Binding Proteins; DNA-Directed RNA Polymerases/physiology; Escherichia coli/genetics; Escherichia coli/metabolism; Escherichia coli Proteins; Formate Dehydrogenases/genetics; Gene Expression Regulation, Bacterial; Hydrogenase/genetics; Lead/metabolism; Molecular Sequence Data; Molecular Weight; Multienzyme Complexes/genetics; RNA Polymerase Sigma 54; Sequence Homology, Nucleic Acid; Sigma Factor/physiology; Trans-Activators/genetics; Trans-Activators/physiology; Transcription, Genetic; Zinc/metabolism |
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