| Summary: | <p>Abstract</p> <p>Background</p> <p>Zinc is considered as an essential element for all living organisms, but it can be toxic at large concentrations. Bacteria therefore tightly regulate zinc metabolism. The Cg2502 protein of <it>Corynebacterium glutamicum </it>was a candidate to control zinc metabolism in this species, since it was classified as metalloregulator of the zinc uptake regulator (Zur) subgroup of the ferric uptake regulator (Fur) family of DNA-binding transcription regulators.</p> <p>Results</p> <p>The <it>cg2502 </it>(<it>zur</it>) gene was deleted in the chromosome of <it>C. glutamicum </it>ATCC 13032 by an allelic exchange procedure to generate the <it>zur</it>-deficient mutant <it>C. glutamicum </it>JS2502. Whole-genome DNA microarray hybridizations and real-time RT-PCR assays comparing the gene expression in <it>C. glutamicum </it>JS2502 with that of the wild-type strain detected 18 genes with enhanced expression in the <it>zur </it>mutant. The expression data were combined with results from cross-genome comparisons of shared regulatory sites, revealing the presence of candidate Zur-binding sites in the mapped promoter regions of five transcription units encoding components of potential zinc ABC-type transporters (<it>cg0041</it>-<it>cg0042</it>/<it>cg0043</it>; <it>cg2911</it>-<it>cg2912</it>-<it>cg2913</it>), a putative secreted protein (<it>cg0040</it>), a putative oxidoreductase (<it>cg0795</it>), and a putative P-loop GTPase of the COG0523 protein family (<it>cg0794</it>). Enhanced transcript levels of the respective genes in <it>C. glutamicum </it>JS2502 were verified by real-time RT-PCR, and complementation of the mutant with a wild-type <it>zur </it>gene reversed the effect of differential gene expression. The zinc-dependent expression of the putative <it>cg0042 </it>and <it>cg2911 </it>operons was detected <it>in vivo </it>with a <it>gfp </it>reporter system. Moreover, the zinc-dependent binding of purified Zur protein to double-stranded 40-mer oligonucleotides containing candidate Zur-binding sites was demonstrated <it>in vitro </it>by DNA band shift assays.</p> <p>Conclusion</p> <p>Whole-genome expression profiling and DNA band shift assays demonstrated that Zur directly represses in a zinc-dependent manner the expression of nine genes organized in five transcription units. Accordingly, the Zur (Cg2502) protein is the key transcription regulator for genes involved in zinc homeostasis in <it>C. glutamicum</it>.</p>
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