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Journal of Bacteriology, May 2008, p. 3482-3488, Vol. 190, No. 10
0021-9193/08/$08.00+0     doi:10.1128/JB.01978-07
Copyright © 2008, American Society for Microbiology. All Rights Reserved.

Regulation of the Bacillus subtilis yciC Gene and Insights into the DNA-Binding Specificity of the Zinc-Sensing Metalloregulator Zur{triangledown}

Scott E. Gabriel, Faith Miyagi, Ahmed Gaballa, and John D. Helmann*

Department of Microbiology, Cornell University, Ithaca, New York 14853-8101

Received 20 December 2007/ Accepted 4 March 2008

The Bacillus subtilis Zur protein regulates zinc homeostasis by repressing at least 10 genes in response to zinc sufficiency. One of these genes, yciC, encodes an abundant protein postulated to function as a metallochaperone. Here, we used a genetic approach to identify the cis-acting elements and trans-acting factors contributing to the tight repression of yciC. Initial studies led to the identification of only trans-acting mutations, and, when the selection was repeated using a transposon library, all recovered mutants contained insertionally inactivated zur. Using a zur merodiploid strain, we obtained two cis-acting mutations that contained large deletions in the yciC regulatory region. We demonstrate that the yciC regulatory region contains two functional Zur boxes: a primary site (C2) overlapping a {sigma}A promoter ~200 bp upstream of yciC and a second site near the translational start point (C1). Zur binds to both of these sites to mediate strong, zinc-dependent repression of yciC. Deletion studies indicate that either Zur box is sufficient for repression, although repression by Zur bound to C2 is more efficient. Binding studies demonstrate that both sites bind Zur with high affinity. Sequence alignment of these and previously described Zur boxes suggest that Zur recognizes a more extended operator than other Fur family members. We used synthetic oligonucleotides to identify bases critical for DNA binding by Zur. Unlike Fur and PerR, which bind efficiently to sequences containing a core 7-1-7 repeat element, Zur requires a 9-1-9 inverted repeat for high-affinity binding.

* Corresponding author. Mailing address: Department of Microbiology, Wing Hall, Cornell University, Ithaca, NY 14853-8101. Phone: (607) 255-6570. Fax: (607) 255-3904. E-mail: jdh9{at}cornell.edu

{triangledown} Published ahead of print on 14 March 2008.

Journal of Bacteriology, May 2008, p. 3482-3488, Vol. 190, No. 10
0021-9193/08/$08.00+0     doi:10.1128/JB.01978-07
Copyright © 2008, American Society for Microbiology. All Rights Reserved.



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